A text sent to parents at around 3pm from Walkden High school reads: “We have been made aware that a man has been approaching girls in the local area to get into the car with him and offering lifts to school.”
Pupils at Harrop Fold High School on Hilton Lane in Walkden have also been warned.
It is understood that three separate incidents in Walkden, Boothstown and Little Hulton were reported to police.
Walkden councillor Iain Lindley said: “This is extremely worrying and all parents and children should be extremely vigilant.
“I hope that the police will be able to apprehend any offenders quickly.
“The pupils who reported this should also be commended for being smart and alert and reporting the incidents straightaway.”
Anyone with any information is asked to call Greater Manchester Police on 101 or Crimestoppers, anonymously, on 0800 555 111. If a crime is in progress please call 999.
Police are continuing to investigate after a 15-year-old girl was attacked and raped in Little Hulton last month
The offender approached the teenage victim from behind near to Cleggs Lane before dragging her into a secluded alleyway and raping her.
Detective Inspector Alan Clitherow issued this video appeal at a formal press conference in Swinton on 14 January.