A bus hit a cargo truck north of Ghana's second city Kumasi overnight, killing 71 people in the West African country's deadliest road crash for years, authorities said on Thursday.

The head-on crash, which left 13 people seriously injured, occurred 420 km north of the capital Accra when a Metro Mass Transit coach bound for the northern town of Tamale from the city of Kumasi hit a truck loaded with boxes of tomatoes, regional police chief Maxwell Atingane said.

"Many of the passengers on the bus died on the spot," Atingane told Reuters. A witness said the scene was "pathetic and gory" with passengers trapped in the bus wreckage. "There were human bodies strewn around," said George Blah, a resident.

Atingane said initial reports suggested a mechanical failure on the bus caused the accident but police were investigating.

Ghana, like many other African countries, has a relatively high rate of road deaths due in part to narrow and poorly constructed roads, failure by drivers to respect speed limits and inadequate vehicle maintenance.

Bismark Owusu Fosu, medical director at the Kintampo hospital, said some of the injured had been evacuated by air for treatment in Kumasi, Ghana's second city. President John Mahama sent a tweet expressing condolences over the deaths.