An overcrowded tourist boat carrying Muslim pilgrims was being piloted recklessly before it capsized, killing at least 18 Thai people.
Divers and other rescuers are searching for 12 people still missing.
The accident happened on Sunday on the Chao Phraya River in Ayutthaya, a UNESCO World Heritage site located some 80 km north of the Thai capital of Bangkok.
The double-decker tourist boat, carrying around 100 Thai Muslims on a pilgrimage, tried to overtake a sand barge and ran into a barrier, police said, causing the boat to capsize.
A police commander said the boat was 50 passengers over its capacity at the time of the accident.
The boat’s driver will be charged with reckless driving causing loss of life and overloading the boat beyond its safety limit.