A powerful earthquake struck Taiwan early yesterday killing at least 11 people, most in a 17-storey apartment building that collapsed, with at least five people missing in the ruins of the complex as darkness fell, government officials said.

As rescuers searched for survivors, questions were raised about the construction of the Wei-guan Golden Dragon Building in the southern city of Tainan, with its floors that pancaked down on each other when the 6.4 magnitude tremor hit at around 4 am, at the start of a Lunar New Year holiday.

Nine of the dead, including a 10-day-old girl, were from the apartment building. The baby was found in her dead father's arms, media reported.

Rescuers mounted hydraulic ladders and a crane to scour the ruins, plucking survivors to safety, with dozens taken to hospital.

An 18-year old man was found alive and conscious shortly after dark, and rescuers were working to get him free, Taiwan television said.

Buildings in nine other locations in the city of 2 million people had collapsed and five were left tilting at alarming angles, a government emergency centre said.

But a fire department official said rescue efforts were focused on the apartment block, where a child's clothes fluttered from a first-floor laundry line and the smell of leaking gas hung in the air.

"I was watching TV and after a sudden burst of shaking, I heard a boom. I opened my metal door and saw the building opposite fall down," said a 71-year-old neighbour who gave his name as Chang.

A plumber, he said he fetched some tools and a ladder and prised some window bars open to rescue a woman crying for help.

"She asked me to go back and rescue her husband, child, but I was afraid of a gas explosion so I didn't go in. At the time there were more people calling for help, but my ladder wasn't long enough so there was no way to save them."

The quake was centred 27 miles southeast of Tainan, at a depth of 14 miles, the US Geological Survey said.

Earlier in the day, an elderly woman, wrapped in blankets, was strapped to a board and slowly slid down a ramp to the ground as the cries of those still trapped rang out. Rescuers used dogs and acoustic equipment to pick up signs of life in the rubble.

Authorities said there were 96 apartment units in the Golden Dragon Building and 256 registered residents. Late in the day, city mayor William Lai said 5 people were missing there.

Rescuers clad in red and yellow overalls pulled 250 survivors from the ruins and later inserted huge supports under slabs of leaning concrete to buttress the ruins as they searched for more.

The fire department said 115 people had been taken to hospital from around Tainan.

City officials said it was too early to determine if poor construction was a factor in the building's collapse.