LUSAKA, Zambia (February 7, 2013)--At least 51 people were killed Thursday when a bus crashed into a semi-truck north of Zambia’s capital of Lusaka, police said.

Police spokeswoman Elizabeth Kanjela said the crash happened Thursday morning in Chifamba, a town about 62 miles north of Lusaka.

Kanjela said the crash involved a bus run by Zambia's postal service, which provides passenger service on buses that also carry the country's mail.

She said police were still investigating the crash and that bodies may still be inside the wreckage.

It wasn't immediately clear what the cause of the crash was, though it happened on a two-lane highway known for having high traffic, even during the night.