The PSNI are investigating reports of a "large explosion" in the Waterside area of Derry just before 5pm today.
Officers have received a number of reports of possible causes of the explosion and are following a number of lines of enquiry. They are trying to establish whether it was linked to a possible attack on security forces.
They are appealing to members of the public in the Waterside area to be extremely vigilant and not to handle any suspicious object.
To investigate the circumstances surrounding the explosion, 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 the Spencers Road at Malvern Terrace and Duke Street. Motorists are advised to expect delays in this area and to allow extra time for their journey tomorrow, especially during the rush hour.
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.
There are no reports of any injuries at this time.
Anyone who witnessed any suspicious activity is asked to contact them on 0845 600 8000.