LANZHOU - Overloading and poor driving have been confirmed as the causes of a fatal bus crash on Friday in Northwest China's Gansu province, said government sources on Sunday.

Investigations found that the bus had left no brake marks at the crash site, a downhill sharp turn on a mountainous road in Ningxian County, Qingyang City, according to the county government.

The vehicle, which was overloaded, caught fire after falling into a ravine at around 10 p.m. on Friday near the county seat of Ningxian.

As of Sunday, 18 people have been confirmed dead and 32 others were receiving medical treatment.

"The bus driver seemed to be oblivious to the road condition as he hadn't even turned his wheel on the stretch, which has consecutive downhill sharp turns," said a traffic policeman working on the accident investigation.

The bus, carrying mostly migrant farmers and their family members, veered off the road at a curve, before tumbling into the 10-meter-deep ravine and catching fire, said sources.

It had a capacity of 47 people, but 54 were on board when it left Langfang City in north China's Hebei Province, according to the provincial emergency response office.

Investigation shows that the overloaded vehicle travelled across four provinces in northwest China to take the migrant workers on their 1,000-km journey back home for the upcoming Spring Festival.

The bus was not stopped by safety authorities and finally crashed about two km away from its destination.

On January 27, China started the world's largest annual migration, which takes place annually before the Lunar New Year.

A record 3.41 billion trips are expected to be made over this year's Lunar New Year travel rush, as Chinese who have worked away from home see the holiday as the most important occasion for family reunions.

Chinese Lunar New Year, or the Spring Festival, falls on February 10 this year, making the holiday travel period span from January 26 to March 6.

However, frequent road accidents have shocked the nation as five traffic accidents occurred in two days from January 31 to February 1. About 60 people were killed in the incidents.

Overloading and poor safety consciousness were mainly blamed as the culprits for the accidents.

Over 100,000 migrant workers from Hebei Province work in Qingyang City. And there is only one licensed passenger bus, with a capacity of 50 passengers, operating between the two cities.

In this context, unlicensed vehicles for long-distance transport have become popular among migrant worker groups.

"It is an annual headache for the family reunion trip. We can hardly ever buy train and passenger bus tickets, and we have to rent a bus with collected money," said Yang Wenwen, who was injured in the bus crash.

The operator of the bus offered poker chips to act as tickets. And the rented vehicle did not set out from a station but from a location chosen by its driver, according to Yang.

"The bus did not receive any safety inspections on the long trip, during which it had run on some expressway sections," he added.