At least 10 children and four women were killed when a boat carrying Rohingya fleeing violence in Myanmar capsized in rough seas off Bangladesh on Thursday, police said.

Witnesses and survivors said the boat overturned just yards from the coast after apparently hitting a submerged object and was later washed ashore in two parts.

"They drowned before our eyes. Minutes later, the waves washed the bodies to the beach," said Mohammad Sohel, a local shopkeeper.

One distraught survivor said he had set off for Bangladesh from a coastal village in Myanmar late Wednesday with his wife, who was killed in the disaster along with one of his children.

"The boat hit something underground as it came close to the beach. Then it overturned," Nurus Salam told AFP.

Around 120 Rohingya, many of them children, have drowned trying to reach Bangladesh in small fishing boats that coastguards say are woefully inadequate for the rough seas.

The United Nations estimates that around 480,000 have fled Myanmar's violence-wracked Rakhine state in recent weeks after attacks by Rohingya militants on security posts prompted a military crackdown.

Local police constable Fazlul Karim said 14 bodies had so far been washed ashore, and there were fears the number could rise.