Taiwan's strongest earthquake in 25 years kills seven, traps 77

• Earthquake kills seven, more than 700 injured

• At least 77 trapped, many in tunnels

• Epicentre just off Taiwan's sparsely populated east coast

• Semiconductor giant TSMC evacuates production lines

TAIPEI, April 3 (Reuters) - 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.

A woman who runs a bed-and-breakfast accommodation in Hualien city said she scrambled to calm her guests who were frightened by the quake.

"This is the biggest earthquake I have ever experienced," said the woman who asked to be identified by her family name, Chan.

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 month, told reporters.

Taiwan's air force said six F-16 fighter jets had been slightly damaged at a major base in the city from which jets are often scrambled to see off incursions by China's air force, but it expected the aircraft to return to service very soon.