KAOHSIUNG, Taiwan -- At least 25 people were killed and 267 injured when underground gas explosions ripped through Taiwan's second-largest city, hurling concrete and cars through the air and blasting long trenches in the streets, authorities said today, as they searched for the cause. 

The series of five explosions about midnight Thursday and early today struck a densely populated district where petrochemical companies operate pipelines alongside the sewer system in Kaohsiung, a southwestern port with 2.8 million people. 

Firefighters called to the neighborhood in the late evening to investigate a gas leak were among the victims when the blasts went off hours later, upending at least six fire trucks in the rubble of pavement and dirt. 

Four firefighters were among the 25 dead as well as some of 267 people injured, the National Fire Agency said. The death toll could rise, because many of the seriously injured were still being treated, officials said. 

Three people also were reported missing in the disaster, Taiwan's second in as many weeks following a plane crash that killed 48 people on July 23. 

"Last night around midnight, the house started shaking and I thought it was a huge earthquake, but when I opened the door, I saw white smoke all over and smelled gas," said Chen Qing-tao, 38, who lives 10 buildings away from the main explosion site. 

The fires were believed caused by a leak of propene, a petrochemical material not intended for public use, but the cause and source of the leak were not immediately clear, officials said.