"We understand that this incident may cause concern for the local community and I would like to reassure residents that there is no risk to members of the public.
"The incident has happened inside a property and those involved are believed to have been known to each other.
"Local officers are out and about in the community to offer reassurance and aid the investigation."
More top news
Emma Jesson brings you Saturday night's forecast
Teaching Assistants have marched through Durham in a dispute over pay. They claim council plans could cost them thousands of pounds.
A team of amateur rowers in Durham say they are lucky to be alive after a heavy object was hurled from a bridge, destroying their boat.