Residents were evacuated from their homes after a car ploughed into a gas flow unit, causing a gas leak.
Emergency services were called to Whitestone Way, Croydon, at about 20:30 GMT on Sunday. The driver stopped at the scene, but was not arrested.
The leak was later fixed but safety checks are ongoing and residents have not yet been able to return home.
A police cordon of 250m remains in place. The incident is not being treated as suspicious.
The car crashed into a gas governor, which regulates gas pressure in a network.
Resident Luke Taylor-Sales said he became aware of "a loud hissing and rushing noise" immediately after the crash followed by a "strong and powerful smell of gas".
He described moving out of his flat as a "saga" but described the police and fire brigade as "impeccable" as they helped residents leave their property.
Engineers are carrying out safety checks on flats.
Residents have been warned they may not have access to heating or hot water when they are initially allowed home.
Energy firm E.On have committed to providing electric heaters to residents.
Croydon Council have set up a rest centre after residents were initially evacuated to a local Sainsbury's store.