Armed police are raiding houses in Moss Side, Manchester, as residents have reported explosions being heard.
One resident said on Twitter there was an explosion near Quantock Close and Selworth Road shortly before 2pm.
Dogs have been seen at the scene and police have closed off roads in the area.
It comes nearly a week on from the attack at Manchester Arena, which killed 22 people and injured dozens more.
One 25-year-old has been arrested as a suspect.
It is still not clear if the explosion was a bomb or a police flash-bang grenade that was used during the raid, although the second scenario seems to be what actually happened, as there is no ambulance mobilization in the area. There is no official report yet.