This is the astonishing moment a piece of flying metal knocked out a trucker as he puffed a cigarette break while driving.

Dashcam footage shows Utthapong Tubtimthong, 42, smoking while travelling in his six-wheeler Nissan when an object shattered through the glass in front of him in Chonburi, Thailand, on September 26.

The shard pierced through his skull, making him lose consciousness instantly, and his vehicle drifted along the road until it crashed.

His truck fell on its side in a ditch before he was rescued and rushed to the hospital.

Amphol Transport 2000 assistant manager Sakmongkol Senjee, and employer of Utthapong, said: ‘The driver was transporting products from Laem Chabang Port to Suvarnabhumi Airport.

‘We are not yet sure where the object came from. We are awaiting details from the police investigation.'

Authorities said they found Utthapong bleeding in the head with a wounded skull and bruises on his chest on the scene.

Rescuers gave him first aid before he was transferred to Chonburi Hospital where he recovered.

An investigating officer said: ‘We will check security cameras at the scene to determine whether it was thrown or bounced off from another vehicle in order to proceed with legal action.'

The trucker's mother Kamonwan Tubtimthong, 63, said: ‘The doctors said his condition will not require surgery but I have not seen his wounds because they don't allow visitors.

‘I hope the police will find out what really caused this.'