BEIJING - A head-on collision between an overloaded van and a coal truck left at least 20 people - including 18 preschoolers - dead and another 44, mostly children, injured on Wednesday. The van, which contained nine seats and had been converted into a school bus of sorts, was traveling in Yulinzi township in Qingyang city, Gansu province, at 9:40 am, when the crash occurred. Sixty-four people were aboard it - 62 children, a teacher and a bus driver - said a statement from the city's work safety bureau.

They were on their way to the Little Doctor Kindergarten in Yulinzi township.

Four children and the bus driver died at the crash scene, and fifteen others were confirmed dead by midday, the bureau said in a news release. Of those who were injured, 13 are in serious conditions.

"The most seriously injured children have been transferred to the hospital in Qingyang city, and the more slightly injured are being treated in the hospital in Zhengning county," said the chief of the province's emergency-management office, who declined to provide his full name.

He said the cause of the accident is still being investigated and the provincial government will hold a news conference later to discuss the latest events in the case.

The General Administration of Quality Supervision, Inspection and Quarantine, the Ministry of Public Security and the Ministry of Education have formed a group charged with investigating the crash. It began that work on Wednesday.

The second vehicle in the crash, the coal truck, bore a license plate from Shaanxi province. The police have detained the person who drove it.

By 4:50 pm, Liu Weizhong, head of the provincial health department, had increased the crash's death toll to 20.

"Doctors have been on their way to Qingyang city and the local blood station has already prepared to offer every blood type," he said.

Vehicles like the van that was in the crash on Wednesday often pick up students who live in rural areas or other remote places and take them to schools. In recent years, increasing numbers of them have been in crashes.

In July 2010, the General Administration of Quality Supervision, Inspection and Quarantine released a regulation meant to make school vehicles that transport primary students safer.

According to the regulation, every school bus must be able to carry at least 10 students, and schools are forbidden from using double-decker buses or articulated buses.

Every bus must also be equipped with a teacher's seat, two emergency exits and a "black box" that can be used to record accident data. Two teacher's seats are required for vehicles that carry more than 40 students, the regulation says.

Only one teacher was aboard the van that crashed on Wednesday.

Why do the regulations not have their intended effects?

"The root cause lies in tight school budgets," said Zhang Yutang, a retired professor of education science at Sichuan Normal University and an expert on student safety.

Xiong Bingqi, deputy director of the 21st Century Education Research Institute, a private, non-profit policy-research body, said many local governments do not set aside money to pay for school vehicles.

Yan Jie contributed to this story.