Euston Station has been evacuated with commuters facing travel chaos ahead of rush hour in central London.
British Transport Police confirmed they were looking into an incident at the busy station amid reports of an "emergency alert".
A spokesperson said: "British Transport Police received a report at 2.46pm today of the fire alarm sounding at Euston Underground station.
"The station was closed as a precaution while London Fire Brigade investigated. Nothing was found and the station has now re-opened."
Passengers just one stop away from Euston were warned that the "station is currently closed" while travelling on the underground.
Others took to Twitter to check on loved ones during the 30 minute evacuation on Thursday.
"Anyone know what happened at Euston Station my little brother just called me saying he's been evacuated?" one person said.
"Anyone in Euston Station know why we’ve all been evacuated?" another asked.
"One tube stop away from arriving at Euston. Announcement “Euston station is currently closed.” Always something with this place," a third added.
Another user said Euston was "not a good place to be right now."
“Entrance to Underground blocked. No explanation for it. Crowded, noisy and confused," they added.
While another claimed that an emergency was “alerted” at Euston station at 2.51pm on Thursday.
Transport for London confirmed that the station reopened at approximately 3.15pm in time for the evening rush hour.
A spokesperson said: "The station and platforms were evacuated this afternoon but all has reopened again now."
Commuters described Euston as "crowded, noisy and confused" with the station set to close over the Easter bank holiday weekend.
Passengers travelling between London Euston and Watford Junction on London Northwestern Railway services have been warned to expect disruption until 4pm.
It comes amid a safety inspection of the track between the two stations.
Euston will close over the Easter holiday weekend from just after midnight on Good Friday until 5am on Tuesday.
Thousands of passengers are expected to face disruption due to the closure.
The station is the sixth busiest in Britain and the busiest passenger route in the UK.
Meanwhile, the West Coast Main Line will be closed between London Euston and Milton Keynes for four days from Good Friday due to upgrades of the existing line and HS2 work.
Rail passengers have also been warned of delays as Network Rail carries out 530 engineering projects costing a total of £83 million.
Parts of the railway between Birmingham International station and Coventry will also be closed, as will lines around Crewe station.
