At least 32 people have been killed and 12 wounded when a tour bus flipped over on a highway near Taiwan's capital, Taipei, according to officials.

Most of the passengers - senior citizens returning from a day trip to a popular cherry blossom viewing site - were trapped underneath the crushed vehicle on an exit ramp in the Nangang district of eastern Taipei, state media said on Monday.

Rescue personnel used a crane to pry the vehicle open.

"It happened on a curve, so the bus flipped and that could be due to excess speed," said Tu Bing-cheng, a Taipei city official.

"The whole frame of the bus changed shape, got crushed and left no openings."

The survivors, some of whom were seriously injured, were sent to hospitals nearby.

Authorities are still trying to determine the exact cause of the accident. Investigators said driver fatigue could not be ruled out, the Apple Daily reported.

A bus driver working for the travel agency that sold the tour told a local broadcaster that some colleagues had previously complained about the tiring assignment.

A bus accident in Taiwan last July killed 26 tourists from mainland China, raising concern from officials in Beijing about travel safety.