A masked gunman walked into a Huddersfield house and shot four people in the early hours of this morning.
The man entered the basement flat in a house on St Stephen's Road in Lockwood at 2.30am and fired his shotgun twice before fleeing the scene.
West Yorkshire Police armed response officers attended the scene where four men aged 26, 18, 25 and 24 were discovered with shotgun injuries to their legs.
The 24-year-old received a serious leg injury and was taken to hospital for surgery.
The 25-year-old was also taken to hospital for treatment but has since been released and all three remaining men were arrested in connection with the incident and are currently in custody.
A woman who lives in an upstairs flat at the same building said she had locked herself in her room.
The woman, who did not want to be named, said she had heard the commotion and the shot-gun blasts.
She said: "I thought we were being broken into at first.
"I said to my boyfriend, 'I think I just heard shots'.
"We were quite scared.
"I couldn't see anything out the window but we hid in our room.
"It took the police about 20 minutes to get here but the helicopter was overhead in about five and was hovering for about an hour."
The woman said the occupant of the flat had only moved in two days ago.
Detective Superintendent Scott Wood of the Homicide and Major Enquiry Team said: "It does appears from our early investigations that this was an isolated and targeted attack.
"We believe a masked man entered the property and discharged a shotgun twice before making away. It is therefore imperative that we find this individual and anyone else involved.
"I would call on anyone who witnessed the incident or has seen any suspicious behaviour around this address prior, to come forward immediately.
"Neighbourhood Policing Team officers are partrolling the area, speaking to residents about any concerns they may have.
"I would urge anyone with information can call us using the non emergency number 101 or Crimestoppers anonymously on 0800 555 111."
Detectives and forensic teams were still on scene this morning, doing house to house inquiries.
Three forensic officers in white suits could be seen investigating inside the property and on the roads around it.
A row of properties next to the shooting scene remains cordoned off and access from Victoria Road is also blocked.