Three people have been killed after two trains crashed into each other between stations in Buenos Aires.

Over 75 people have been injured and many had to wait for rescue workers to pull them from the wreckage.

Four area hospitals were treating the injured, including some with exposed fractures.

The two-level train slammed into the back of the other train between the stations of Moron and Castelar on the Sarmiento line, which links the Argentine capital's densely populated western suburbs to the downtown Once station.

It was not immediately clear why the leading train had stopped between stations, and why the train behind failed to stop in time.

Because the accident happened on the outbound tracks, the cars were much less full of passengers than those carrying commuters to work in the city.

Union leader Ruben Sobrero said the two-level train had been out of service for six months and was brought back online shortly before the accident.

Pablo Gunning, a spokesman for the government-run agency said the engine had new brakes installed and had been approved for service.

After last year's wreck at the Once station, which also injured 700 people, President Cristina Fernandez promised to prosecute those responsible and make new investments in safety.

She revoked the concession run by Mario and Sergio Cirigliano, two brothers who own many companies involved in maintaining Argentina's rail systems, and formed a state-supervised consortium of companies to operate the commuter lines.