At least 27 people died and more than 20 others were injured late Monday when a bus careered off a hillside road and into a ravine in northern Thailand, police told AFP.

At least 27 people died and more than 20 others were injured late Monday when a bus careered off a hillside road and into a ravine in northern Thailand, police told AFP.

Thailand's roads are among the world's deadliest and accidents are common, especially on buses travelling late at night.

"The toll is now at 27 dead and 24 injured -- they are severely injured from what I can see," police captain Sittichai Panyasong of Mae Tho district in Tak province said, revising up an earlier toll.

The accident took place at around 8:40 pm local time (1340 GMT) in Tak, which borders Myanmar, as several buses ferried Thai local government workers to neighbouring provinces for a field trip.

"The brakes failed as the bus came downhill on a hilly road and it crashed through the concrete barrier and fell into 150 metre-deep ravine," Sittichai added.

The victims are mainly believed to be local government officials but a child was also among the injured, he said.

A spokeswoman at a local hospital, declining to be named, confirmed the death toll at 27 adding she also believed there were children on board.

Thailand's roads are among the most dangerous in the world.

A recent report by the World Health Organization said Thailand saw 38.1 road deaths per 100,000 people in 2010 -- behind only the Dominican Republic in the Caribbean and the South Pacific island of Niue.

That compares with an average of 18.5 per 100,000 in Southeast Asia as a whole.

At least 13 school children died last month when their bus collided with a lorry on trip to the seaside south of Bangkok.

The students, aged around 10 to 14 years old, were heading to the resort city of Pattaya from the northeastern province of Nakhon Ratchasima.

Officials say roughly 60 percent of traffic accidents in Thailand are caused by human error, with poor road and vehicle conditions posing additional hazards.

Bus operators are required to provide seat belts but passengers are not legally obliged to use them.

In December dozens of people were killed when a bus carrying New Year travellers plunged off one of Thailand's highest bridges in the kingdom's northeast.

At least 20 people were killed in October when a tour bus carrying elderly Buddhist devotees fell into a ravine, also in the northeast.