DETECTIVES probing links between a carjacking and an attempted burglary at a house have warned owners of expensive cars to be on their guard against gangs.

In the latest attack on motorists, a 56-year-old woman was robbed of the keys to her £25,000 Mercedes at knifepoint by a masked gang as she took money out of a cash machine. It came five days after a homeowner fought off four men at his house on Hill Crest - quarter of a mile away.

In both attacks in the Over Hulton area of Bolton, the victims were threatened by men brandishing knives.

Police fear gangs are targeting vulnerable drivers to snatch keys because anti-theft systems on expensive cars make them almost impossible to steal.

Det Chief Insp George Fawcett, head of Bolton CID, said: "It's obvious that criminals are looking for other ways of stealing vehicles due to the increased security of cars.

"Carjacking offences are very traumatic for the victim and motorists are reminded to lock their car doors when driving in the evening or at night time and to keep valuables and bags out of sight if possible.

"I wish to warn motorists to be vigilant at this time, but also reassure them that officers from the robbery unit and CID have worked to ensure that offences of robbery have fallen by 30 per cent in Bolton over the past year."

The woman was approached by four men wearing balaclavas as she took money out of a cash machine on Newbrook Road, Over Hulton on Tuesday night.

It was the third incident of carjacking since the start of the year in Bolton.

Det Chief Insp Fawcett said officers had also noted a rise in "sneak in" burglaries where car keys were the target of thieves and warned homeowners to make sure houses were secure.