A boat carrying about 70 Rohingya Muslims has capsized off the western coast of Myanmar, with eight survivors found so far, according to an aid worker.

Abdul Melik, who works for the humanitarian organisation Action Against Hunger, said the boat was in the Bay of Bengal and headed for Bangladesh when it went down early on Sunday morning.

Families of the missing people kept watch on the beach throughout Sunday, said Aung Win, a leader of the Muslim Rohingya community.

"I saw people waiting there to find dead bodies," he told Reuters by phone from the state capital, Sittwe.

The incident comes after the United Nations warned that an annual and often deadly exodus of desperate people from Myanmar's Rakhine state appears to have begun.

The exodus usually kicks off in November, when seas are much calmer.

The UN High Commission for Refugees said on Saturday that as many as 1,500 people have fled in the last week and that there were several reports of drownings.

Rohingya have been leaving Myanmar in droves since clashes with ethnic Rakhine Buddhists, who make up the majority of the state's population, erupted in June and October last year.

The government said at least 192 people died in the violence and the United Nations says about 140,000 people remain in camps.

The vast majority of those killed and displaced were Rohingya and growing numbers are now making treacherous journeys by boat to countries including Malaysia and Indonesia.

Many have been in Rakhine state for generations, but the government considers them illegal immigrants from Bangladesh and severely limits their movements.