The station doors have been closed while large crowds of people gather outside on the cold streets of London.
Frustrated passengers took to social media to describe the chaos, with some suggesting the evacuation had taken place due to overcrowding.
One Twitter user posted: “Whole of #kingscross underground evacuated in an emergency. Not sure why. Huge crowds leaving at rush hour.”
Another tweeted:”#KingsCross evacuated in rush hour. Surprisingly everyone was quick getting out.”
“Kings Cross evacuation is likely due to ‘overcrowding’ – Londons transport system is basically obsolete and not fit for purpose,” a commuter added.
Others laid into Transport for London (TfL), claiming the overcrowding problems were now a regular occurrence.
One commuter said: “There must be a better way to close Euston without causing panic by announcing an emergency on repeat, needlessly scary.
Another added: “Scary evacuation at Euston underground. Why are staff shouting head to the exit as quickly as possible?
“Evacuation announcement on a loop”.
Video filmed by passengers show sirens being sounded over the PA system along with a message telling people to leave the station.