Police said they were looking into media reports linking the raid to a Saturday night attack in which three people drove a van into pedestrians on London Bridge before stabbing revellers nearby. Police did not confirm the two incidents were related.
Sky News also reported that four men and one woman had been detained during the raid in Barking, east London, which was launched at 0700 by armed police.
A Reuters witness described a heavy police presence and a cordon around a block of flats as residents of other flats in the building looked out from their windows onto the scene.
An eyewitness to the raid told Sky he heard several bangs during the operation and was later told they were controlled explosions used to gain access to the building.
(Reporting by Hannah McKay and William James, editing by Estelle Shirbon)
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)