Niamey (AFP) - Niger will from Wednesday observe three days of mourning for 60 people who were killed in a tanker truck explosion near the international airport in the capital Niamey, the government said.

The days will pay tribute "to the memory of the victims of the tragic accident" that occurred early Monday as crowds had gathered around the overturned truck to collect spilt fuel, according to an interior ministry statement read out on state television late Tuesday.

Earlier, security official Hamani Adamou Abdoul-Aziz told state television the toll from the explosion would likely rise because several people sustained severe, life-threatening burns.

Interior Minister Mohamed Bazoum said people on foot and motorcycle had rushed to the truck to take fuel when the blast occurred. According to witnesses, one biker failed to switch off his engine, causing a spark that ignited the 50,000 litres of fuel.

The driver of the tanker truck has told investigators that an electrical failure caused him to lose control of the vehicle and its brakes.

The truck overturned as he tried to bring it to a stop, senior police official Boubacar Rabiou Daddy told a TV station.

Before the blast, people ignored police trying to keep them away, and threw stones at firefighters, he added.

The massive explosion on the RN1 route near the international airport left the burnt truck's wreckage, motorbikes and debris scattered over the road.

Nearby houses were damaged by fire.

About 40 people were reported injured, most of them in a very serious condition in hospital with severe burns.