Nine homes have been evacuated and an area cordoned off in a Buckinghamshire town after an anti-terror raid by police overnight on Wednesday.
Police seal off a wooded area near Micklefield Road in High Wycombe
The operation in the Walton Drive area of High Wycombe was "as a precautionary measure", Thames Valley Police said.
One person from High Wycombe is among 24 being questioned about an alleged plot to blow up transatlantic flights.
Two other houses in the town have been raided and specialist teams are searching an area of King's Wood.
This area is close to Micklefield Road, where the two properties were raided by police.
Officers have blocked the road off and are guarding the scene.
Supt Mike Ismay said there was not thought to be a direct threat to people in the High Wycombe area.
Total: 24 people arrested
London: 'Majority' of arrests - exact locations not known
Birmingham: Two arrests
High Wycombe: At least one arrest
He said: "The investigation, which will be complex and lengthy, is still at an early stage."
Speaking about the evacuation, he said: "This is standard practice in operations of this kind and there is no need for anyone to be alarmed."
He said police were unsure how long it would be until residents could return home.
Tory MP Paul Goodman, whose constituency includes High Wycombe, said it was an "inexpressibly sad day" for the town, where community relations were "traditionally good".
All the people arrested are accused of preparing to detonate liquid explosives smuggled on board planes.
The threat level to the UK was raised by MI5 to critical after the arrests.
Critical threat level - the highest - means "an attack is expected imminently and indicates an extremely high level of threat to the UK".