Pinned to the floor by the scruff of its neck, this helpless guide dog makes a desperate effort to get away as it is savaged by a pit bull.

Rather than pull it away, the pit bull's owner can be seen punching and kicking his animal in a futile attempt to end the attack.  At one point he even ran off.

He eventually managed to drag the dog away - but only after it had inflicted deep puncture wounds on the black labrador's neck.

The attack took place as the guide dog's owner, a 57-year-old blind woman was walking through Cricklewood station, in north-west London.

She passed close to a man standing in an underpass who was drinking a can of beer with the dangerous dog at his feet.

At that point, the unleashed animal ran towards her and launched the attack on her dog, forcing her to let go of the lead.

The incident was caught on CCTV and police hope the images will help trace the owner.

The owner of the pit bull fled and is being hunted by police

Instead of helping comfort the shaken blind woman, the cowardly pit bull owner abandoned her and fled from Cricklewood Station in London.

PC Gerry Griffin said the ordeal, which left the owner deeply upset, lasted three minutes.

He said: 'This dog was not muzzled and was dangerously out of control. The woman was extremely distressed and feared for her own safety.

'What made this awful incident even more harrowing was the fact that the man made no effort to assist her or to check that she was all right once the attack was over.

'We have carried out a number of local inquiries and ask that anyone who recognises the man gets in contact with us.

'The owner would do well to hand himself in as his animal poses a clear danger to other dogs and to the public.'

The blind woman's dog, which cost thousands of pounds in charity donations to train, was left with a neck wound.

Police said they were trying to trace the man and his dog, which was brown with white paws and a white tip to its tail.