Published Tuesday, 10 January 2012
The noise was reported in the Waterside area of the city just before 5pm on Tuesday.
A statement from the PSNI said: "Police have received a number of reports of possible causes of the explosion and are following a number of lines of enquiry.
"An attack on police is one possible line of enquiry."
Unconfirmed reports suggest the bang came from the Spencer Road area.
Residents there have now been evacuated "for the safety of the local public" amid ongoing investigations, and road closures put in place.
The statement continues: "Police are evacuating the area around Spencer Road.
"Fountain Hill, Spencer Road and the minor roads between Chapel Road and Spencer Road will be closed and it is believed that these will be closed until sometime tomorrow to allow for daylight searches.
"Diversions will be in place on Spencer Road at Malvern Terrace and Duke Street.
"Houses in Dunfield Terrace and Moore Street are also being evacuated for the safety of the local public. The Clooney Hall on Clooney Terrace will be available for evacuated residents to go to."
No injuries have been reported and the cause of the sound has not been determined.
Local SDLP councillor Gerard Diver told UTV it may have been a device exploding.
"I'm hearing various theories as to what has happened," Mr Diver said.
"There are unconfirmed reports at this stage saying there may have been some sort of device that has been detonated or fired and I would imagine that the most likely target would have been the police."
Officers have warned people in the area to be "extremely vigilant" and asked them not to touch any suspicious objects they may find.
Anyone with information is asked to pass it on.