(BBC) At least 53 people have been killed in a crash involving a bus and lorry in Zambia, police say. The death toll could rise as rescuers were still trying to get into the bus wreckage hours after the crash, police reportedly said.

The accident occurred about 100km north of the capital Lusaka on a two-lane highway known for heavy traffic. Poorly maintained and overloaded vehicles are commonplace in Zambia. Nonetheless, this is said to be one of the worst traffic accidents in the country's history.

According to reports, the bus was operated by the Zambia Postal Service, which provides passenger services on buses which carry post, and was full of people.

'Bus swerved'

It crashed into a lorry - and according to Zambia's information minister Kennedy Sakeni a sports utility vehicle was also involved in the crash, the Associated Press news agency reported.

The wreckage of the bus was so mangled that hours later emergency workers were still trying to get into it to check for victims, police spokeswoman Elizabeth Kanjela was quoted as saying.

There was serious speeding by all the vehicles involved, Harry Kalaba - an official in the vice-president's office - told AFP news agency from the crash site.

A survivor was quoted as saying the bus had been swerving to avoid an oncoming vehicle.

Some 22 dazed or unconscious survivors were being treated in a nearby missionary hospital, AFP said, while more seriously injured casualties had been taken to hospital in Lusaka.

President Michael Sata conveyed his government's "deepest condolences" to families of the victims. Police are investigating the cause of the crash.

In 2005, 44 schoolchildren were killed when the vehicle they were travelling in crashed in northern Zambia.