A 24-year-old man has been killed after an e-cigarette blew up in his face and severed a major artery as he vaped for the first time.

William Brown, from Fort Worth in Texas, was using the device in his car outside the Smoke & Vape DZ store in North Fort Worth on January 27, just moments after purchasing it, according to his grandmother.

Shrapnel from the exploding pen penetrated his left carotid artery in his neck, cutting off blood to his brain.

The electrician is thought to have crawled from his vehicle and tried to get help before collapsing on the sidewalk.

He was taken to John Peter Smith Hospital, where he was declared dead two days later.

The Tarrant County medical examiner listed the cause of death by 'penetrating trauma from exploding vaporizer pen'.

His grandmother Alice Brown said her grandson was not a regular smoker and had bought the specific type of pen because he was told it could help ease his asthma.

Mrs Brown said investigators have told her it was the battery that caused the explosion.

'It just hurts so bad, now he'll never see that birthday. It's a waste of the things he could have accomplished,' she told the Fort Worth Star-Telegram.

'It just all seems so unreal. He was running around doing his thing at 24 and now he's gone.'

A staff member at the vape store said Mr Brown didn't purchase the device from the shop, according to Dallas News.