A petrol thief is raising eyebrows in Ngaio.

Ngaio residents are being urged to check their cars for the smell of fuel following a strange string of petrol thefts.

Over the past two weeks there has been three cases in the area where thieves have severed vehicles' fuel lines.

Inspector Clint Walker said it's an unusual ploy to siphon petrol.

"That was concerning for a number of reasons. More importantly the vehicles user, their safety is a major issue but relatively unusual."

Inspector Walker said residents should be extra vigilant, especially if their cars have been parked on the street overnight.

"If they do smell fuel around their vehicle after a night of being parked then they just need to be cautious. Check the car and just see what's happening."