A train carrying 800 passengers smashed into a truck at a level crossing in southern Russia on Monday, sending at least eight carriages off the track and injuring 52 people, local authorities said.

Authorities in Volgograd region said 21 people remained in hospital after the collision, involving a train travelling from Kazan in central Russia to Adler on the Black Sea.

Previous reports had put the number of injured at about 140.

Russian Railways had earlier reported that the driver of the train slammed on the brakes when he saw the Kamaz truck, whose driver had broken traffic rules and entered the crossing despite alarms.

The train hit the truck at about 65 kph (40 mph) near Kotelnikovo station, about 1,200 km (750 miles) south of Moscow.

The driver of the Kamaz, who was thrown about 15 metres (50 feet) by the impact, was in a grave condition, said the Mash Telegram channel, which published video showing the battered remains of the cabin of the truck and a man whom it said was the driver with blood on his face.

Video published by state news agency TASS showed carriages derailed, some of them twisted.

Russian Railways said more than 300 passengers had resumed their journey aboard one train while another train had arrived in Volgograd region to take the rest.