At least 34 people were killed and dozens injured in two separate road accidents Saturday, each in places where collisions had taken place shortly before, local media reported.

A first crash involving a bus and an ambulance killed 15 people and injured 31 more on a motorway in Gaziantep province, said local officials, revising an earlier toll of 16.

Governor Davut Gul said earlier the accident had involved "a bus, an emergency team and an ambulance" on the route between provincial capital Gaziantep and Nizip.

The DHA news agency said a passenger bus had crashed into an ambulance, a firefighting truck and a vehicle carrying journalists at the site of a previous crash.

Three paramedics, three firefighters and two journalists from Turkey's Ilhas news agency were among those killed, local media reported.

Photos on DHA showed the back of the ambulance ripped out and damage to the bus.

Gendarmes are currently questioning the driver of the bus to try to establish what happened, DHA reported.

Prosecutors are already investigating a second deadly accident a few hours earlier, 250 kilometres away (155 miles) away, which also happened as the emergency services were attending an earlier incident at the site.

On this occasion, at least 19 people were killed and nearly 30 injured after a truck driver hurtled into pedestrians at Derik in Mardin province, Health Minister Fahrettin Koca wrote on Twitter, updating an earlier toll of 16.

The accident in Derik in Mardin province "occurred after the breaks gave out on a lorry, which hit a crowd", Koca wrote. Another 26 were injured, six of them seriously, he added.

Turkish media shared footage of a driver losing control of his truck, then careening towards nearby vehicles and pedestrians as they try to flee.

Turkey's official Anadolu press agency reported that an accident involving three vehicles had happened at the same site shortly before. Emergency responders were already at the scene when the lorry ploughed into crowd.

Justice Minister Bekir Bozdag announced on Twitter that prosecutors had opened two investigations into the accidents.

"All resources are mobilised," he wrote on Twitter, offering his condolences to those who had lost ones.

President Recep Tayyip Erdogan has sent Interior Minister Suleyman Soylu to the site of the accident and he was expected there later Saturday, the Anadolu agency reported.