Seven people were injured in an explosion at Croydon Police station, believed to have been caused by accident during building works in the station firing range.
Around 100 police officers and 14 prisoners were evacuated to South Norwood Police Station after the incident on Tuesday morning. The station was back to full operation at 10pm on Tuesday.
Four of the seven injured were contractors working on the site. One was airlifted to Broomfield Hospital in Chelmsford, where he is described to be in a serious condition.
Another man was taken to St Georges hospital where he remains in a stable condition.
It is understood the other three have been discharged.
Police have confirmed the explosion occurred in the firing range area, which has recently been decommissioned to allow for refurbishment, and was not due to reopen until May.
Chief Inspector Caroline Trevithick said police had ruled out that a gun or weapon had caused the blast.
Borough Commander Dave Musker, said: Our thoughts and good wishes are with those who have been injured and we continue to liaise with the London Fire Brigade and the Health and Safetly Executive to establish the cause.”