At least 20 people were killed and more than 70 injured after a subway train derailed in Mexico City late on Monday.

Forty-nine people have been taken to hospital after the accident, said the city's mayor - who also gave the updated death toll.

Videos on Mexican television and social media showed train cars hanging in mid-air as sirens blared nearby. Footage on Milenio TV showed the overpass collapsing on to cars on a road below.

Emergency crews and firefighters have been searching through the train for survivors and at least one car has been buried by rubble.

Another video showed emergency medical crews and firefighters at the scene of the accident combing through wreckage looking for survivors.

Mexico City’s mayor, Claudia Sheinbaum, said on Twitter that a support beam had given way, causing the overpass to collapse. She said that “firefighters, public safety personnel are working. Various hospitals attending. We will give more information shortly.” She said 34 people had been sent to hospital.

The accident happened at 22.30 local time (4.30 UK time) on the metro's Line 12 - the construction of which has been plagued with complaints and accusations of irregularities.

Rescue efforts were paused at around midnight as a crane was brought in to stabilise the partially hanging train amid fears it could fall further onto the road.

Meanwhile friends and relatives of people believed to be involved have gathered at the scene near Olivos station, in the southern borough of Tlahuac.