A fire ripped through a bus carrying tourists from China in Taiwan Tuesday, killing all 26 on board in the worst road accident to hit mainland visitors since a holiday boom to the island.

The disaster, which occurred as the tourists were heading to the airport for their flight home, was the latest in a series that have called into question Taiwan's safety record.

Media footage showed the bus, with flames shooting from the front, rammed into an expressway barrier near Taipei.

The images showed thick plumes of smoke and burned-out wreckage at the roadside.

A police spokesman said the bus had caught fire before it crashed into the barrier but gave no reason.

"All the people on the bus died," Lin Kuan-cheng, spokesman for the National Fire Agency, told AFP.

"At this stage it is still not clear why no passengers escaped from the bus."

The Liberty Times newspaper quoted an unnamed eyewitness as saying passengers were pounding on the bus windows for help as the driver swerved sharply before the crash.

One image in Hong Kong's South China Morning Post newspaper showed two men trying to smash the windows of the burning bus with fire extinguishers as the doors of the vehicle remained shut.

A firefighter at the scene said there were no survivors still calling for help when they arrived.

The bodies were being retrieved from the vehicle Tuesday evening after police and prosecutors examined the site, said an AFP photographer at the scene.

The tour group of 24 people -- three children, 15 women and six men -- was from China's northeastern city of Dalian, Taiwan's interior ministry said.

A Taiwanese driver and Taiwanese tour guide were also killed, the National Fire Agency confirmed.

The group were on their way to Taipei's main Taoyuan airport for a 4:30 pm flight back to Dalian after an eight-day tour of the island. The accident happened shortly before 1:00 pm.

- String of accidents -

Chinese tour groups have increasingly visited Taiwan in recent years after a boom in mainland tourism.

That was fostered by a rapprochement between the rivals under former Taiwanese President Ma Ying-jeou, who came to power in 2008 and left office in May.

However, there are fears the industry may be hit after Beijing-sceptic Tsai Ing-wen won the presidency in January, amid reports that tourist numbers have dropped.

China's Taiwan Affairs Office said it had launched "emergency response measures" after the accident, and would send a team to the island to help handle the aftermath.

"We are highly concerned about the safety of our mainland compatriots," said spokesman Ma Xiaoguang, quoted by state news agency Xinhua.

Several recent fatal accidents in Taiwan have led to safety probes.

In February 2015 a TransAsia plane crashed into a river in Taipei, killing 43 on board -- including 28 mainland Chinese tourists. A recent report by investigators confirmed the pilot had shut down the wrong engine after the other one failed. The airline was instructed to overhaul safety procedures and training.

In June 2015 coloured corn starch sprayed over crowds at a water park party near Taipei ignited due to the heat of stage lights, killing 15 and injuring more than 500 -- many of them young people who sustained horrific burns. The organiser of the event was jailed for negligence.

The collapse of a residential block during an earthquake in the southern city of Tainan in February this year, which left 115 dead, led to an investigation which showed builders had cut corners.

The previous worst road accident to kill Chinese tourists was in 2010 when a tour bus was hit by a landslide following a typhoon on a coastal road in the east of the island, leaving 20 dead.