An investigation is under way after a Tube train entered a tunnel the wrong way, into the path of another train.
One of the drivers has been stood down
Hundreds of passengers were on each of the two Northern Line trains when the incident happened on Sunday.
The driver is believed to have slammed on the brakes when he saw the other train, which had stopped at a signal at Camden Town station.
He has been stood down during the probe into the incident, a Transport for London (TfL) spokesman said.
"A formal investigation into the incident involving a Northern line train is now well under way," the spokesman said.
"Incidents of this nature, whilst disturbing to the public, are incredibly rare."
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