At least 13 people have died in a boat accident on Thailand's Chao Phraya river after it slammed into a bridge and sank.

The two-floor crowded passenger vessel went down on Sunday near the ancient city of Ayutthaya, about 80km north of the capital Bangkok.

"There are 13 confirmed dead and 33 injured so far," said Udomsak Khaonoona, disaster prevention chief for the city.

"The boat tried to avoid another vessel and crashed into the concrete column of a bridge," he told the AFP news agency.

Accidents are common in Thailand's transportation networks [EPA]

About 100 passengers were believed to be on board the vessel, with four currently unaccounted for, Udomsak said. 

Video footage posted by Khaosod TV showed desperate scenes as rescue workers scrambled to reach the boat, its lower deck submerged under water.

Rescuers threw ropes to help people swim to land as others gave CPR to unconscious victims on the banks of the river. 

The Chao Phraya, the main river that flows through Bangkok, is a key commuting artery, often packed with boats plying the waterways at breakneck speed.

Accidents are common on Thailand's public transport network as safety regulations are often weakly enforced.

The country has one of the world's worst road traffic death rates, and crashes between speedboats connecting the popular southern tourist islands are common.

Source: News Agencies