BANGKOK (AFP) - The captain of a boat that sank on a swollen river in central Thailand did not have a valid licence, an official said on Tuesday (Sept 20), as the death toll rose to 26 and included several children.

The accident happened on the Chao Phraya river on Sunday afternoon near the ancient city of Ayutthaya, when a boat packed with Muslim pilgrims returning from a mosque hit a concrete bank in strong currents.

The boat, which was carrying double its 50 passenger capacity, sank in seconds.

Ayutthaya Deputy Governor Rewat Prasong said the captain faces charges including having an expired licence, allowing too many passengers on board and negligence that led to death.

The toll rose overnight to 26 with eight children confirmed among the dead.

"We are still looking for three people - two women and a girl - who have been reported missing by relatives," he said.

Safety regulations are poorly enforced in Thailand, including on boats, with overcrowding, sinkings and crashes common - particularly in busy tourist areas.

According to the World Health Organisation, Thailand has the world's second highest road fatality rate after Libya.

The Thai junta has got tough on breaches of many laws, but has yet to addressed chronic safety lapses in the country's transport system.

But the dire safety record has not deterred tourists from visiting the kingdom.

Nearly 30 million visitors did so in 2015, a number boosted by a surge in mainland Chinese tourists.

The junta expects tourism to account for as much as 17 per cent of gross domestic product this year.