Police say they've tracked down the phone and two girls they believe are responsible for making 60 fake calls to 911 over four weeks this summer.

Public information officer Rob Carver said the calls caused a "massive drain on resources."

Two girls, one 12 and the other 15, were arrested Wednesday in connection with the prank calls.

"It's not just the responding officers. Our [communications] centre dispatchers take these calls incredibly seriously.... To find out that level of stress is based on an unfounded call is very distressing," Carver said.

The calls, which also threatened police, were made between July 26 and Aug. 23, he said. All were treated seriously, with police going to the same downtown Winnipeg residence, and sometimes multiple cars responded.

None of the calls were determined to be actual emergencies, said Carver.

Police received the most recent call, which led to the arrests, on Wednesday.

The 911 caller said an adult female had been stabbed. Emergency responders determined the claims were unfounded and found the cellphone used for dozens of fake calls.

Police charged the two girls with public mischief. The 12-year-old faces additional charges for allegedly assaulting an officer during the arrest as well as two counts of uttering threats.

"We hope that it does send a message that this is a huge drain resources and that it is a criminal offence and charges will be laid," said Carver.

Locating the phone that made so many unfounded emergency calls was difficult, Carver said. It was the downtown general patrol that finally cracked the case.

"They did an excellent job in sorting this out and putting an end to a problem that really had plagued the service for the better part of a month," Carver said.