A man was taken to hospital after he was attacked during a robbery at a house in Lynn.
An invesitgation has been launched into the incident, which happened in Friars Fleet, Ethel Terrace, at around 7pm last Thursday, June 16.
However, detectives have stressed they believe it to be an isolated incident.
Three men are said to have entered the property, threatening two male occupants before demanding money.
Two men were assaulted in the incident, one of who needed hospital treatment as a result.
The raiders left the scene with a camouflage cotton rucksack and a small amount of cash.
Detective Inspector Teresa Futter said: “We believe this to be an isolated incident.
“However, I would urge anyone with information about the incident to contact the police.”
She added: “I would like to reassure members of the public that incidents like this are rare in Norfolk.”
Anyone who may have seen or heard anything suspicious in the area between the times stated or anyone with information should contact Det Con Chris Parnham, of Lynn CID, via the non-emergency 101 number.
Alternatively, contact the independent charity Crimestoppers anonymously on 0800 555111 or use their online form at www.crimestoppers-uk.org