The Olympic torch was lit in Bangkok on Saturday, and set off on a route around the city, flanked by Chinese security officers, amid tight security.
Thai authorities had beefed up security ahead of the torch relay, deploying 2,000 police to protect the Olympic flame from protesters.
The 10.5-kilometre (6.3-mile) relay started in Bangkok's Chinatown and will end at the Royal Plaza, although the route may be changed or shortened at the last minute if protesters try to disrupt it.
Growing criticism of China's human rights record have turned the Olympics - which begin in August in Beijing - into one of the most contentious in recent history.
Protests over China's crackdown on Tibetan demonstrations against Beijing's rule have dogged the torch relay at various stops on its worldwide journey that began at the ancient site of the original Olympics in Greece.
A coalition of human rights and other activist groups in Thailand held a protest outside the U.N.'s Asian headquarters, which is on the planned relay route in Bangkok.
A counter-protest by Chinese supporters was also held outside the UN building, but the two groups were kept apart and there was no trouble between them.
On Friday, Prime Minister Samak Sundaravej said his government could provide adequate security and warned crowds not to try to disrupt the relay.
The torch arrived by plane on Friday under tight security and was quickly whisked off to a luxury hotel.
Thailand's crown princess welcomed the flame shortly after its arrival.
The torch was scheduled to leave for Malaysia on Saturday night.