Taiwan's biggest earthquake in at least 25 years killed seven people on Wednesday, injuring more than 700, with 77 trapped in tunnels and collapsed buildings, authorities said, as rescuers used ladders to help some people descend to safety.

Television broadcast images of buildings tilted at precarious angles in the mountainous, sparsely populated eastern county of Hualien, near the epicentre of the 7.2 magnitude quake, which struck just offshore at about 8 a. m. (0000GMT).

"It was very strong. It felt as if the house was going to topple," said Chang Yu-lin, 60, a worker in a hospital in Taipei, the capital.

The quake hit at a depth of 15.5 km (9.6 miles), just as people were headed for work and school, setting off a tsunami warning for southern Japan and the Philippines that was later lifted.

Video showed rescuers using ladders to help trapped people out of windows, while elsewhere there were massive landslides, as strong tremors in Taipei forced the subway system to close briefly, although most lines resumed service.

Fire authorities said about 60 of the roughly 77 trapped were caught in a tunnel just north of Hualien city, with two Germans among those trapped in another tunnel.

The government put the number of injured at 736.

"At present the most important thing, the top priority, is to rescue people," said President-elect Lai Ching-te, speaking outside one of the collapsed buildings in Hualien.

The rail link to the area was expected to re-open on Thursday, Lai, who is set to take office next mnonth, told reporters.

In Japan, the weather agency put the quake's magnitude at 7.7, saying several small tsunami waves reached parts of the southern prefecture of Okinawa, while downgrading its tsunami warning to an advisory.

In the Philippines, seismology officials warned coastal residents in several provinces telling them to move to higher ground.

Chinese state media said the quake was felt in the southeasterrn province of Fujian, while a Reuters witness said it was also felt in the commercial hub of Shanghai.

Aftershocks could still be felt in Taipei, with more than 50 recorded, weather officials said.

Most power has been restored after the quake, electricity utility Taipower said, with the island's two nuclear power stations unaffected.

Taiwan's high-speed rail operator said no damage or injuries were reported on its trains, although services would be delayed as it made inspections.

A major supplier of chips to Apple and Nvidia , Taiwan Semiconductor Manufacturing Co, said it had evacuated some fabrication plants and safety systems were operating normally.

"To ensure the safety of personnel, some fabs were evacuated according to company procedure," the semiconductor giant said in a statement, adding later that the employees had begun to return to work.

Taiwan's benchmark share index closed down 0.6%, largely brushing off the quake's impact, while TSMC's Taipei-listed shares ended down 1.3%.

The official central news agency said the quake was the biggest since one of magnitude 7.6 in 1999 that killed about 2,400 people and damaged or destroyed 50,000 buildings.

Taiwan weather officials said the intensity of the earthquake in Hualien county was at the second-highest level of "Upper 6" on an intensity scale from 1 to 7.

Such a quake collapses walls unless they are made of reinforced concrete blocks, while people cannot stand upright and must crawl in order to move, Japan's weather agency says.