Cape Town: A bus carrying worshippers headed to an Easter festival has plunged off a bridge on a mountain pass and burst into flames in South Africa, killing at least 45 people, authorities said.

The only survivor of the crash on Thursday (Friday AEDT) was an eight-year-old child, who was airlifted to hospital, according to authorities in the northern province of Limpopo. They said the child was seriously injured.

The Limpopo provincial government said the bus veered off the Mamatlakala bridge and plunged 50 metres into a ravine before busting into flames.

Search operations were ongoing, the provincial government said, but many bodies were burnt beyond recognition and were still trapped inside the vehicle.

Authorities said they believed the bus was travelling from the neighbouring country of Botswana, a landlocked country, to the town of Moria, which hosts a popular Easter pilgrimage. They said it appeared that the driver had lost control, causing the bus to go over the bridge and hit the ground where it caught fire. They believed the driver was among the dead.

Minister of Transport Sindisiwe Chikunga was in Limpopo province for a road safety campaign and changed plans to visit the crash scene, the national Department of Transport said. She said there was an investigation underway into the cause of the crash and offered her condolences to the families of the victims.

The South African government often warns of the danger of road accidents during the Easter holidays, which is a particularly busy and dangerous time for road travel. More than 200 people died in road crashes during the Easter weekend last year.