Kaohsiung Mayor Chen Chu said that the incident was the worst of its kind in recent decade, Xinhua reported.
The island's fire-fighting authority said gas leaks were reported in the city's Cianjhen district at around 9.00 p.m. on Thursday, leading to multiple explosions that affected an area as large as three square kilometres.
Jiang Yi-huah, the island's executive chief, is coordinating the rescue operations at an emergency response center that was put into operation early on Friday.
The island's military force has deployed more than 300 soldiers to the sites to carry out rescue work.
Meanwhile, Taiwan leader Ma Ying-jeou has urged relevant authorities to help the rescue, his office spokeswoman MaWei-kuo said.