BANGKOK – At least six passengers including three foreigners died after a tourist ferry sank on Sunday off the Thai resort of Pattaya, police said, amid fears people may still be trapped in the stricken vessel.

"There are six dead – three Thais and three foreigners," a police official told AFP, without giving details on the nationalities of the foreigners.

The ferry sank on Sunday afternoon near Koh Larn, a small island off the Pattaya coast popular with daytrippers.

Local reports said the vessel may have been overcrowded and listed after experiencing engine trouble.

"Police received a phone call from relatives of the passengers on the ferry," the police officer told AFP, requesting anonymity.

"We are rescuing them... we are not sure whether there are people still trapped inside (the ferry)."

There was no immediate confirmation of the number of injured or missing, but local media said dozens of ambulances had been called to Pattaya's beachfront to handle casualties being plucked from the water.

A Pattaya Tourist Police spokesman said there were an estimated 100 passengers on the boat, which ran into engine trouble at about 5pm local time (1100 GMT).

Pattaya is around 150 kilometres (100 miles) south of Bangkok.

Russian news reports said three Russians, including a child, had been taken to hospital in a serious condition.

"At least half of the passengers were Russian tourists," Russian consul in Bangkok Andrey Dvornykov was quoted as saying by the Ria Novosti news agency.

Renowned for its racy nightlife and cheap accommodation, Pattaya is one of Thailand's most popular resort areas and has become wildly popular as a package holiday destination for Russians.

Thailand drew 22 million tourists last year, but is struggling to shake off a reputation for lax safety standards after a series of fatal incidents.

In recent years the kingdom's tourist-friendly image as "the Land of Smiles" has also been tarnished by political violence and devastating floods.

Four people died in a nightclub fire in August 2012 on the party island of Phuket, while there have also been several high-profile cases of foreigners being murdered in recent months.

Diplomats from China and the European Union have voiced concern at the number of fatal incidents involving tourists in Thailand either due to accidents or crime.

In July, an American tourist was allegedly stabbed to death by three Thai musicians after he refused to stop singing at a bar. His death followed the murder of another US citizen in a row with a taxi driver in Bangkok.