Officials say a double-decker bus carrying municipal workers on a field trip plunged off a steep road into a ravine in western Thailand, killing at least 30 people.

The accident happened on Monday evening in Tak, which borders Myanmar, as several buses ferried Thai local government workers for a field trip to Laos.

Tak’s provincial governor Suriya Prasatbunditya said 22 people were injured in the crash that occurred when the driver tried to pass other cars on a steep, winding mountain road.

The driver, who survived the accident with a broken rib, said he tried to slow down but claimed the brakes stopped working, according to Suriya.

"The brakes failed as the bus came downhill on a hilly road and it crashed through the concrete barrier and fell into a 150-metre deep ravine," a local police captain, Sittichai Panyasong, told the AFP news agency.

Suriya said there were more than 300 accidents on the same road last year.

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

A recent report by the World Health Organisation said Thailand saw about 38 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.

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

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

Source: Agencies