At least 20 people have been killed after a minibus struck a landmine in Guinea-Bissau, a doctor who treated several victims said.

Augusto Blute said on Saturday that the bus was travelling between the towns of Bissora and Encheia in the north of the country when the explosion occurred on Friday.

A police source, who asked not to be named, told the Reuters news agency that 19 people were killed on the spot when the blast tore the vehicle in two and three others died of their injuries overnight.

Local officials say the mine may date to the country's fight for independence from colonial power Portugal in the 1970s.

There was no immediate statement from the government.

The country obtained independence in 1974, though it has been roiled by coups and instability since then and no president has ever completed his term in office.

Guinea-Bissau held elections earlier this year meant to draw a line under the country's last coup in 2012.

The new government is trying to push through a raft of reforms, including breathing life into a declining economy and asserting civilian authority over the military, which has a history of interfering  in politics and cocaine trafficking.

Source: Agencies