Farringdon station has been evacuated and closed due to a suspected gas leak, with a “small number of passengers reporting feeling unwell”.
British Transport Police (BTP) was called to the station at 09:42 BST and the incident is also affecting train services.
BTP said: “Officers are in attendance, alongside the ambulance service and the fire brigade, and the station has been evacuated while enquiries are conducted.”
National Rail has advised passengers that there will be no services at Farringdon until 13:00.