Thames Valley Police is investigating an aggravated burglary in Milton Keynes.
Shortly after 12am yesterday (Sunday) offenders knocked at the door of a property in Yarrow Place, Conniburrow.
When an occupant opened the door, three of the offenders barged past him and entered the property, while a fourth stood outside.
Some of the offenders went upstairs and threatened a female occupant of the property with a knife and stole cash from her.
As the offenders were leaving, a male occupant of the property was hit in the head with what is believed to have been a firearm.
The victim, a man aged in his twenties, was taken to hospital with non life-threatening head injuries.
All of the offenders are men, three are described as black and the fourth offender is white.
Detective sergeant Phil Turner-Robson, said: “Detectives are currently working to establish the circumstances of this aggravated burglary.
“Officers have been completing house to house enquiries in the area as part of our efforts to identify and locate the offenders.
“If anyone saw anything suspicious in the area or perhaps saw a commotion at the door of a house in Yarrow Place at around the time of the incident, I would ask they contact police as the details may be helpful to the investigation.
“People in the community may notice officers patrolling the area and if anyone has any information or wishes to raise any concerns, they can speak to an officer in the area or call our non-emergency number 101.”