Two light commuter trains collided Tuesday in the southern part of Mexico City injuring 20 people, the municipal government announced.

The crash, which occurred about 7 a.m., apparently resulted when one of the trains stopped on the track due to a malfunction and was hit from behind by the other train.

The crash seriously injured 27-year-old Cesar Munguia, one of the trains' drivers, and slightly injured 19 other people. All of the injured were taken to hospitals.

The trains, which have just two cars each and a maximum carrying capacity of 374 passengers, are part of the Federal District's Electric Transport Service, or STE, and they only operate in the southern part of the capital along a route comprised of 16 stations and two terminals.

"The emergency (authorities) attended to the incident in a timely way," the STE said.

At the accident site, efforts are under way to remove the damaged trains and quickly resume commuter rail service.

The trains will be taken to the network terminals, where their black boxes will be recovered so that authorities can determine the causes of the accident.