Police are continuing to question 10 people arrested following a series of anti-terror raids.
A forensics officer removes a bag from one of the premises
Six men and one woman were held in Manchester and three others elsewhere.
They were arrested under the Terrorism Act 2000 on suspicion of involvement in the commission, preparation or instigation of acts of terrorism.
More than 400 police from the
Greater Manchester, Staffordshire, West Midlands and South Yorkshire forces took part in the operation.
Security services and the Metropolitan police anti-terrorism branch were also involved.
The arrested people were of North African or Iraqi Kurd origin, Assistant Chief Constable David Whatton of Greater Manchester Police told BBC News.
He described the arrests and searches as "part of an ongoing operation looking at the threat of terrorism across the whole of the United Kingdom."
He said it would also continue in the future, but
"it is something the public has become aware of as we have done some overt activity".
"This is working against the background that we've never had a such a high level of threat from terrorism in the United Kingdom since some time before Christmas," ACC Whatton said.
ACC Whatton said speculation that public buildings in Manchester were targets for terrorists was "extremely unhelpful" and urged the public to be vigilant.
A spokesman for the Home Office said it would be "inappropriate" to comment on police inquiries while they were ongoing.
He said: "We cannot get into a running commentary on the intelligence and information behind police and security services operations, as to do so would undermine counter-terrorist work.
"We have always said that we would not hesitate to issue a warning if it is the best way to protect the public in respect of a specific and credible threat."
Three properties close to Manchester city centre remained cordoned off on Monday afternoon while forensic officers inspected them.
The cordon included AK Computers, Dolphins takeaway and Funky Fones on Upper Brook Street.
ACC Whatton said searches would probably continue into Tuesday.
The properties are three storeys high, with the top two storeys of each converted into flats.
Officers in protective clothing entered the takeaway, while two police officers stood guard at the rear of an upstairs flat.
At the front, four police officers stood around the cordon.
The road outside the flats remained open to traffic.
Police have not said where the 10 people are being held.