Sixty seven people were reportedly hospitalized after the engine of a crowded Bangkok commuter boat exploded Saturday. The ferry was transporting passengers on a major canal in the eastern outskirts of Thailand’s capital, which uses an extensive network of waterways to transport goods and people in motorized boats.

Most of the injured were suffering from burns, local media reported, citing police officials. While a majority of those hospitalized were later released, 14 were reportedly still receiving treatment.

An initial police investigation suggested the blast was caused by a fuel leak on board, police officials said. The explosion, which occurred slightly after dawn, shook the wooden boat but left the hull largely intact. Bangkok's police commissioner Sanit Mahathavorn reportedly said two passengers were seriously hurt by flying debris from the explosion.

Witnesses interviewed on Channel 3 — a Thai news channel — described a loud bang that rang out just as the boat was docking, sending some passengers racing for the pier while others leapt into the canal's murky waters.

"We still don't know how it exploded," the director of Family Transport, the private company which operated the boat, told the channel, adding that the boats have been using gas-powered engines for up to eight years.

In the meantime, the company's 25 boats, which run on diesel and liquefied natural gas like the boat which exploded, were ordered to use only diesel for now.

Canal boats, which cost less than $1 for a ride, are popular among locals as one of the cheapest and fastest ways to travel around the traffic-choked capital city.