Residents have been evacuated from their homes in Leyland after bomb disposal teams were alerted to an incident.
The security operation started this morning after reports of a man with a suspicious device at a property in Mendip Road.
Bomb squad officers have been sent to the scene and local residents have been evacuated to South Ribble Tennis Centre and the nearby Hayrick pub.
Some parents have collected their children from nearby Manor Lane Primary School although officials say the school remains open despite the police operation.
Donna Hamilton, 36, lives next door to the house where officers are focusing their investigation. She said: “At about nine o’clock this morning I saw all the police down the street.
“They got some step ladders and put them up against the flat. I got told to get out.”
Mum-of-two Laura Burns, 22, Mendip Road, was one of the residents evacuated. She said: “I got a knock on the door at about 11 o’clock this morning.
“I saw the police from my window and went to see what was going on. I was told to get out my house and take my kids with me.
Kirsty Bayley, 28, has a child at nearby Lancaster Lane Primary School.
“I heard about what was happening so went to pick up my child. I didn’t want to take any chances.”
Eddie Stevenson, 23, lives with his 47-year-old dad on Mendip Road, said: “I came out the house and wasn’t allowed back in.
“I can see loads of police and there are some at the back of the house with shields looking like they’re about to go in.”
Lancashire Constabulary would not confirm details of incident but said officers were dealing with a “police incident.”
A spokesman for Lancashire Police said Mendip Road and Hunters Road had been closed for “safety reasons”. Police attended the scene at 10am on Friday and the roads were closed soon after.