The 23-year-old woman was walking to her car at an Aldi car park in Bolton at 5.45pm on Friday when she noticed a man on his phone who seemed lost.
He asked her where he was and she helped him by giving the person he was speaking to on the phone their location.
As she got into her car, the man, who called himself Kevin, asked her for directions to the Ikon nightclub and she offered to give him a lift.
She dropped him off on Duke Street, near the Salvation Army building, and the man thanked her and opened the car door as if to leave.
It was at this point he suddenly grabbed her handbag from the back seat.
The woman tried to grab him as he made off and the man fell over.
The victim then got out of her car and started wrestling with the man as she tried to retrieve her bag.
During the struggle, she was struck on her head several times.
She screamed, the man ran off and she realised she was covered in blood.
The woman was taken to the Royal Bolton Hospital, where she was given 20 stitches.
Police believe she was attacked with a meat cleaver.
Detective Inspector Andy Meeks, of Bolton CID, said: "This was a shocking and needless attack on a young woman who was being extremely generous to someone she thought was lost.
"It has left her with quite serious injuries and feeling terribly shaken."
The man was white, aged between 25 and 30, 5ft 6ins to 5ft 10ins tall, of stocky build with a squashed nose and stubble.
He was wearing a dark hooded top with light sleeves.
Following the attack, he ran away towards the Salvation Army, leaving the woman's bag behind.