Armed police were called into Huddersfield after a man was stabbed.
The firearms officers sealed off a maze of streets in Aspley as the man was taken to hospital, as there were reports of a gun being seen.
The injured man has been stabbed in the arm but his injuries are believed to be non life-threatening.
The West Yorkshire Police helicopter was also flown in to join the hunt, as at least one man fled the scene in a car.
The incident happened shortly before 4pm in Garforth Street, which is close to the River Colne at Aspley.
The injured man was found in nearby Colne Street with serious wounds and was today detained in Huddersfield Royal Infirmary.
At the scene, police inquiries centred on a semi-detached house in Garforth Street but large parts of Day Street and Colne Street were also cordoned off with blue and white police tape.
One eye-witness said: “It happened so quickly.
“All of a sudden there were six or seven police cars and vans pulling up in the streets.
“I saw a lot of police officers and a few of them had weapons and what looked like body armour.”
Another eye-witness added: “The man was stabbed in the arm, his right arm I think and clubbed in the head. It all started in the house and spilled out into the street. There were children playing around.”
Police were seen checking tyre marks in the street close to the former Flyboat pub.
Shortly after 4.30pm, the helicopter flew into Huddersfield and for several minutes hovered over the Leeds Road area of Bradley.
Det Insp Stef Wiseman, of Kirklees CID, said: “It is early days and we have a lot of inquiries to make.
“The injured man’s injuries are not life-threatening but he is at the hospital, having been found in Colne Street. We believe he got there from Garforth Street.
“A car was seen leaving the area and the helicopter was asked to help in a search for that vehicle.
“A number of lines of inquiry are being followed up and we would appeal to any witnesses to come forward.”