Search operations resumed on Monday for missing passengers a day after a boat carrying Muslims for a religious trip capsized in Thailand’s Chao Phraya river in Ayutthaya province. The confirmed death toll was 15, but local media reported that 18 passengers were killed in the incident.

The double-decker boat was carrying about 100 passengers — 50 more than its authorized capacity — police commander Surapong Thampitak told Reuters. The vessel reportedly tried to overtake a sand barge and hit a concrete pillar, causing it to sink.

Surapong reportedly said that police will charge the boat’s driver — taken into custody Sunday night —with reckless driving resulting in loss of life and carrying excess passengers beyond the safety limit. Apart from the driver, two others have been summoned for investigation and they face the same charges as the driver. If found guilty, they could receive up to 10 years in prison.

The boat was making a return journey from a memorial for a Muslim scholar at amosque in Ayutthaya. No foreigners were reported among the victims.

“We are searching for around 11 missing people today,” Ayutthaya Deputy Governor Rewat Prasong reportedly said Monday.

The Chao Phraya river flows through Bangkok, where it is used as an important commuting route and is often packed with fast boats. The river also runs through Ayutthaya, the ancient Thai capital where its sides are lined with remains of old Buddhist temples.