A man died on the floor of a department store during the US's busiest shopping day - and other shoppers reportedly ignored him.

Walter Vance, 61, was buying Christmas decorations at Target just after midnight when he collapsed from a heart attack.

Witnesses saw shoppers walk around and over Mr Vance's body, WSAZ TV in West Virginia reported.

An off-duty nurse and paramedic eventually came to Mr Vance's aid, but he died after being taken to hospital.

The world was outraged last month when a Chinese toddler was run over by a car and ignored by passers-by.

Black Friday is considered the beginning of America's Christmas shopping season and has recently been the country's biggest day for retail sales. It follows the Thanksgiving holiday.

Shoppers often compete fiercely for bargains and this year was notable for its violence.

A woman at a Los Angeles Walmart pepper-sprayed other shoppers to beat them to marked-down Xbox consoles, the LA Times reported. Twenty people were injured.

Police are deciding whether to lay charges against the woman, described only as being in her mid-30s.

Elsewhere in the US, shoppers scuffled over discounted bath towels, mobile phones and waffle irons. Several shootings were also reported. Many of the scenes were recorded on mobile phones and have been put up on YouTube.

A 54-year-old grandfather in Arizona was thrown face-first to the ground by police after they allegedly saw him put two computer games under his shirt.

"It was like a bowling ball hitting the ground, that's how bad it was," one witness told CNN.

Video of the man lying unconscious on the ground and bleeding profusely from the face has gone viral. Onlookers heckled police as they handcuffed the man and mopped blood from his face. "That's police brutality, man," one can be heard saying.

The man has been charged with resisting arrest and shoplifting. Police have said they will investigate the incident.

Some witnesses say the man put the games into the waistband of his pants so that he could free his hands and lift his grandson above a stampeding crowd.

This year's Black Friday drew record sales. Americans spent $US52.4 billion ($53.53 billion) over the Thanksgiving weekend, up 16 per cent compared to last year, the National Retail Federation said.

- Sydney Morning Herald