Just before 7:00 pm (2200 GMT), a long-distance train rammed a local train that had emerged from the Retiro station, which connects the federal capital with populated north and northwest suburbs, officials said.

"There are four dead and 14 seriously injured," said Buenos Aires province governor Daniel Scioli.

Local fire chief Oscar Ferrari earlier said rescuers had freed survivors who had been trapped in the wreckage.

"There are no more people trapped," he told reporters, adding that the crash pushed several rail cars together, killing and wounding passengers in the rear of one of the trains.

San Miguel Mayor Joaquin de la Torre regretted a "catastrophic" situation and said he could not recall a train accident in at least two decades in the area.