Three knife-wielding masked raiders disrupted a children’s birthday party when they burst into a house demanding drugs.
Police believe the men, who threatened people inside the house in Norwich, broke into the wrong address.
Officers were called to the property in Hunter Road, Catton Grove, at about 18:50 GMT on Friday, Norfolk Police confirmed.
No one was hurt, but a mobile phone was stolen, the force said.
The men are described as black, about six feet tall (183cm) and were wearing dark clothing.
“This must have been very distressing for those involved and I want to reassure the victims and those that live locally that we are doing everything we can to find the offenders quickly,” Insp Graham Dalton said.
“I do believe this is connected to Operation Gravity drug dealing and would ask anyone with information regarding those involved to contact the police immediately.”
Operation Gravity is a Norwich Police campaign, launched in 2016, to deal with drug dealers coming into the county from London.