Five men have been arrested under the Terrorism Act including a 62-year-old from Bolton.
Officers from the North West Counter Terrorism Unit arrested the men in a co-ordinated operation starting at 4am today, Greater Manchester Police said.
A house in Willows Lane, Deane and four in Manchester are currently being searched, a force spokesman said. The others are in Stalybridge, Stockport Road, Levenshulme, Victoria Terrace, Longsight, and Bowdon Avenue, Fallowfield.
The spokesman added: "People living in nearby communities will see a high profile police presence during the day and will be able to discuss issues with local officers.
"This was a low-key operation and no armed officers were involved.
Assistant Chief Constable Dave Thompson said: "Protecting people both at home and abroad is our primary concern which is why we take such steps.
"This is a complex and ongoing investigation, which has now reached the point where it was necessary to make arrests and speak to a number of people.
"There was no direct threat against Greater Manchester and the arrests are the latest stage of a thorough investigation. We have been liaising with local people to provide reassurance about what has happened and will continue to keep a high profile presence in affected areas.
"Officers will also be distributing letters around the areas concerned and speaking to residents to let people know what has happened and to ask them to continue to work with us in the coming days.
"The community will be concerned that these arrests caused disruption and distress to people living there. There is no suggestion that those other people were involved in any offences and our priority is to look after these people."
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