The mood among opposition supporters in Istanbul is one of jubilation, mixed with worry, as their apparent narrow win in mayoral elections could be overturned after President Recep Tayyip Erdogan's governing party challenged the results, prompting a recount.

In an unexpected setback to the president, the opposition appeared to have won Sunday's tight race in the city, the country's financial and cultural capital where Erdogan himself rose to power as mayor.

Joy over candidate Ekrem Imamoglu’s razor-thin win has given way to concerns after the ruling Justice and Development Party, or AKP, contested results in all of Istanbul’s 39 districts, alleging fraud and demanding a recount of votes deemed invalid.

Electoral authorities, whose independence opposition parties have questioned in the past, allowed recounts in at least 18 districts.

A senior AKP official on Thursday said the gap in votes had now further narrowed to around 19,000 - from around 25,000 announced on Monday.

The AKP has put up posters around Istanbul featuring pictures of Erdogan and the AKP's candidate, former prime minister Binali Yildirim, and thanking residents for their support - a move that many regard as a premature declaration of victory.  

Yildirim himself had declared victory on Sunday, before acknowledging that Imamoglu had a narrow lead.

Imamoglu himself tweeted on Friday he was leading by 18,742 votes.

His backers denounce what they see as two sets of rules for the ruling party and the opposition, recalling that similar appeals by their secular Republican People's Party were derided and rejected in past elections.

Meanwhile, opposition parties’ appeals for at least two tightly contested races elsewhere were also rejected.    

In Istanbul’s fashionable Cihangir neighbourhood, 60-year-old antique dealer Huseyin Guney expressed concerns that victory would be wrested away from the opposition.

"If Imamoglu has won justly, if it has been fated... If it isn’t, and if other avenues are pursued, our country’s image will really be shaken," he said.

Media organs close to Erdogan have claimed that AKP votes were stolen as part of an alleged "coup" against the ruling party, whereas international observers said the election was not fair.

Imamoglu, a 49-year-old former businessman and the little-known mayor of the Istanbul district of Beylikduzu, led a good-humoured campaign during which he promised to build bridges in the highly polarised city.

He even visited Erdogan in Ankara and asked for his vote too.

But he drew ire among AKP officials for signing a visitor's book at the mausoleum of Turkey’s founder in Ankara as "The Mayor of Metropolitan Istanbul" before the election results are finalised.

Istanbul - 4 April 2019

1. Various of people walking on a bridge over the Golden Horn, banners of Turkey's President Recep Tayyip Erdogan and ruling AK Party's Istanbul mayoral candidate Binali Yildirim (Turkish) 'Thank you Istanbul'

2. Woman sitting on the shore of the Golden Horn, Haghia Sophia in the background

3. Traffic on a street

4. Billboard of Turkey's President Recep Tayyip Erdogan and ruling AK Party's Istanbul mayoral candidate Binali Yildirim (Turkish) 'Thank you Istanbul'

5. Saban Ozmen's upholstery shop

6. Close of door 'Ozantik chair upholstery'

7. Saban Ozmen upholstering a chair

8. Close of staple gun

9. SOUNDBITE (Turkish) Saban Ozmen, Istanbul voter:

"People are fed up. I don't know, someone new brings excitement. I think he'll (referring to Ekrem Imamoglu) work (for the city.) The others thought they had settled by staying so long (referring to ruling AK Party.) It's not how it should be. A new excitement is necessary, someone who's willing to work. People have rights and I think that was being exploited."

10. Ozmen upholstering an ottoman

11. Close staple gun

12. SOUNDBITE (Turkish) Saban Ozmen, Istanbul voter:

"Everyone must show respect. I think he (Imamoglu) will be successful at the job. May it bring good fortune. God willing there will be no unrest."

13. Various of Huseyin Guney outside his antique shop

14. SOUNDBITE (Turkish) Huseyin Guney, opposition supporter:

"If Imamoglu has won justly, if it has been fated, it (Istanbul's mayorship) should be given to him. If it isn't, and if other avenues are pursued, our country's image will really be shaken. After all it's a local election and (Erdogan) still runs the country."

15. Various of people walking on the street

16. SOUNDBITE (Turkish) Erhan Celik, AK Party supporter:

"Whatever comes out of the vote, a full democracy is always the best for us, we defend a full democracy. Irregularities occur in elections, they have occurred, are occurring, and there are mechanisms against this and those will be set in place. But for example I didn't approve of what Imamoglu did: signing Ataturk's (mausoleum) visitor's log as 'mayor.' He could have waited a few more days, if it's his right (the mayorship.) Because you are nothing until you are given the (formal) mandate."

17. Wide of voter Semih Gokdemir having tea

18. Close of table

19. SOUNDBITE (Turkish) Semih Gokdemir, Istanbul voter:

"As I said, change is always good. The five-year process (length of mayoral mandate) will bring many things. During that time we'll have the opportunity to re-evaluate, favourably or unfavourably. But I believe that changes, different perspectives, will always move a place forward because competition is important. Monopolies are always problematic. At least now there's an environment of competition. We'll see the favourable and unfavourable aspects in the days to come but it's a hopeful situation for us."

20. Various of marine traffic on Golden Horn

Turkish President Recep Tayyip Erdogan will on Friday inaugurate Istanbul's third and longest cross-continental bridge over the Bosporus.

The Yavuz Sultan Selim bridge links the city's Asian and European sides, includes a rail line connecting the two continents, and aims to ease traffic in the highly congested city of nearly 15 million.

Transport Minister Ahmet Arslan told The Associated Press that the construction of the 215 kilometres (134 miles) of highway and the suspension bridge cost 3.5 billion US dollars.

The bridge's name has been the source of some controversy.

Ottoman sultan Selim I, known as "Selim the Grim" in English, is said to have killed thousands of Alevis, a Muslim Shiite sect in mostly-Sunni Turkey.

But Arslan said the bridge was "not discriminatory".

Instead, the "unifying" structure was a symbol of Turkey's aim to "protect and look after everyone".

Former transport minister Binali Yildirim, now the country's prime minister, is also expected to attend Friday's ceremony.

Istanbul - 23 August 2016

1.Tilt (down) of Yavuz Sultan Selim Bridge

2. Close of a sign next to the bridge reading (Turkish) "The new pearl of the Bosphorus"

3. Low angle panoramic shot

4. Mid of bridge

5. Turkish and Transportation Ministry flags, Istanbul's Bosphorus and skyscrapers behind

6. Mid of bridge

7. Fire engine driving on the bridge

8. Worker driving construction equipment on the bridge

9. Workers on the bridge

10. Wide of Ahmet Arslan, Turkish transport minister arriving

11. Close of Arslan

12. SOUNDBITE (Turkish) Ahmet Arslan, Turkey's transport, maritime and communications minister:

"We are talking about a 10-lane suspension bridge which at the same time includes a railway, giving trains the possibility of passing over (between Asia and Europe). This is a first, and a record in the world with its 59 metre (200 foot) width. This is a project that has 322 metre (1.050 foot) long towers, and a 1,408 metre (1 mile) span. If we consider its construction, this is a project that is admired by engineering authorities and that breaks many records."

13. Wide of the bridge

14. SOUNDBITE (Turkish) Ahmet Arslan, Turkey's transport, maritime and communications minister:

"If you think about Istanbul's two existing bridges (the fact that we are) moving heavy vehicle circulation to this bridge will ease transportation and also the life of every Istanbul resident. And, it will decrease the negative influence of automotive emissions over a historical city like Istanbul, the cradle of many cultures."

15. Wide of Bosphorus behind Yavuz Sultan Selim Bridge

16. SOUNDBITE (Turkish) Ahmet Arslan, Turkish transportation, maritime and communications minister:

"Beginning from Yavuz Sultan Selim (an Ottoman Sultan) we conserve and protect all of our historical assets. These historical assets are not discriminatory, to the contrary, they are unifying. Yavuz Sultan Selim, Haji Bektash Veli (Alevi mystic and philosopher) no matter what his/her language is, religion, race or sect, we want to embrace everyone who lives in the country, in Anatolia. We want to embrace everyone and within this context, retrospectively all of their leaders and chiefs are an asset for us. We conserve and protect all of our assets. And with this bridge we protect (the memory of) Yavuz Sultan Selim. This is not discriminatory. On the contrary, this is unifying and a symbol of the fact that we protect and look after everyone. I think that this is how it should be considered."

17. Mid of the Bosphorus Bridge behind the Yavuz Sultan Selim bridge

18. Tilt (down) of the bridge

Istanbul - 3 August 2016

19. Various of Yavuz Sultan Selim Bridge

20. Various of two people sitting on a hill, bridge behind

21. Pan (right to left) of the brigade

22. Wide of the Bridge from Sariyer district of Istanbul's European side