At least 23 people were killed and 15 others injured when a tanker truck exploded as it was negotiating a downhill mountain road in the southern Philippines, police officials said Friday.

The truck apparently lost its brakes, slammed into the side of a mountain and overturned, killing the driver, said Senior Superintendent Ramon Ochotorena, police chief of Zamboanga del Sur province.

He said witnesses accounts and documents recovered from the scene indicated the tanker was carrying compressed carbon dioxide gas. An initial police report said it was carrying liquefied petroleum gas.

Passing motorists and passengers of a minibus that was following the truck tried to help extricate other truck crewmen on the highway in the town of Tigbao, he said.

Minutes later, someone shouted there was a fire from beneath the truck, but before people could flee, the tanker exploded with such force that it completely demolished the vehicle and blew away the roof of the bus and flung it to the opposite lane, Ochotorena said.

"It was blown to smithereens. You cannot see any parts of the truck here," Ochotorena told The Associated Press by cell phone from the site, about 480 miles south of Manila. "Fortunately, there were no houses nearby."

Click here for more Asia stories on FOXNews.com.