TAIPEI (AFP) - Taiwan on Thursday (July 28) ordered almost half the tour buses inspected after a recent bus inferno - which killed dozens of Chinese tourists - off the road after they failed new safety checks.

Twenty-four Chinese tourists and two Taiwanese nationals died in the fire earlier this month, the worst road accident ever to hit mainland visitors to the island - raising major safety questions.

Nine of 20 buses of the model which caught fire have been taken off the road due to problems with circuit fuses and storage batteries, highway department officials said on Thursday.

Three more such buses had minor issues, which the authorities have ordered be repaired.

The bus, operated by the Mei Kui Shih Transportation Company, caught fire and smashed through an expressway barrier last week, just a few kilometres from Taipei's Taoyuan Airport.

Taiwanese prosecutors are probing the exact cause of the disaster and say the fire started at the front of the bus, near the driver's seat.

Questions have also been raised over the driver's mental state after five bottles of gasoline were found in the bus - despite regulations banning inflammable substances in a vehicle.

"We have twice searched residences of the driver and looked into his medical records to clarify his mental state prior to the accident," said Mr Wang Yi-wen, a spokesman for the Taoyuan district prosecutors' office.

The driver's relatives and co-workers are also being questioned, he added.

Distraught relatives of the Chinese victims have questioned why no one was able to escape through the emergency exits when the fire ripped through the bus.

Pictures from the scene showed two men outside the bus trying to smash windows open with fire extinguishers.

One eyewitness said trapped passengers inside the bus had been pounding on the windows as it careered off the road.

Chinese officials have demanded Taiwan take measures to ensure the safety of mainland visitors to the island.

The accident is expected to deal a further blow to cross-strait tourism, with China ties already becoming increasingly frosty since new Beijing-sceptic President Tsai Ing-wen took office in May.

Taiwan's official data showed the number of Chinese tourists dropped 16 per cent in May-July 2016 compared to the same period last year, with speculation that Beijing is putting pressure on Ms Tsai by squeezing tourism.