Television programmes are to be interrupted to broadcast appeals for help in tracing abducted children.
Police say the public will be alerted "quickly and accurately"
Child Rescue Alert will ask the public to aid the search to find a kidnapped child where it is feared the victim will be seriously harmed or killed.
The system was being rolled out across Cumbria, Cheshire, Merseyside, Greater Manchester, North Wales and the Isle of Man on Monday.
The scheme is based on a successful American system called Amber Alert.
Amber Alert was created after nine-year-old Amber Hagerman was kidnapped in Arlington, Texas, and then murdered.
Since its launch in 1996, more than 311 children in the US have been recovered and returned to their families.
Police forces involved in the scheme will work closely with broadcast media outlets across the North West to ask members of the public to report possible sightings of missing children.
A special telephone number will be published and extra staff brought in to ensure any information is acted upon quickly.
Ass Ch Con Mike Cunningham, of Lancashire Constabulary, said the system was going to be a "fantastic tool".
"However, I must point out that speed will need to be balanced by appropriate checks to ensure we don't overuse the system," he said.
"We want the public to understand that we will only launch a CRA in truly exceptional circumstances. That way, if they hear one they will immediately appreciate just how serious it is.
"I believe it will be a valuable resource that will almost certainly help the police during such sensitive and time-critical investigations.
"Thankfully, this type of crime is rare, but I am convinced CRA is a major step forward in helping us combat it."