A fire that ripped through a hospital in Japan as patients slept killed 10 elderly people Friday and prompted government demands for safety reviews across the country.

The blaze, which broke out in the middle of the night, left a further five people injured, police said, with the fire and disaster management agency saying four of them were in a serious condition.

Video footage aired on public broadcaster NHK showed firefighters surrounding the hospital in the city of Fukuoka, in the southwest, as smoke poured from the front entrance of the partially gutted building. Dark streaks of soot were smeared across the second floor windows.

"We have confirmed the deaths of 10 people -- eight in-patients and two hospital workers," said a local police spokesman. The two hospital workers were a former hospital director and his wife, police later said.

All of those who died were between the ages of 70 and 89, police said.

The fire raged for around two hours, having started at 2:20am (1720 GMT) at the four-storey building, which opened as an orthopaedic hospital in 1970.

The hospital has 19 beds, with suites for orthopaedics, rheumatism and rehabilitation.

Hospital staff lived on the top floor, a local fire station official said.

"We did our best in fire fighting to save lives... but it was a difficult situation," a fire station official told a hastily arranged press conference.

"We received news of the fire at a very late stage, and there had been no attempt (by staff) to tackle the fire in its early stages," he said.

"Patients on the second and third floors were exposed to a lot of smoke because fire doors that would have stemmed the flow had been left open," he said, referring to the first and second floors in British English.

"We will start an investigation" into the cause of the fire, the official said.

Thermal therapy equipment

Another fire station official told AFP that the fire appeared to have begun somewhere on the ground floor, but he did not know the specific place or cause of the fire.

"We first received the report of a fire after a nurse who was inside the hospital rushed out and asked a taxi driver to make an emergency call," he added.

Local media reported the fire may have started at a treatment room which had a laser device and thermal therapy equipment that used a water boiler.

Hours after the tragedy, Japan's fire and disaster management agency issued administrative guidance to fire headquarters nationwide that officials check hospitals to ensure medical organisations are prepared for nighttime fires.

It also sent seven officials to the scene to probe the cause of the disaster, an agency spokesman said.

NHK quoted a firefighter as saying the building was already belching flames and smoke when fire engines arrived.

A 43-year-old woman living in the neighbourhood told the network: "A lot of smoke came to the front door of my house and I heard shouts like 'Help!' and crunching sounds."

A man who lives in the neighbourhood told private broadcaster Nippon TV that the ground floor "was red with flames and was filled with smoke. The part where beds were located seemed to be burning".

He said he had seen some elderly patients being rushed out of the burning building, with ambulance crew performing heart massage.

Private broadcaster TV Asahi said around 20 fire trucks had attended the blaze.

Latest television footage showed dozens of police and fire department officials conducting on-site investigations.

While Fukuoka is a fairly modern city, in common with other parts of Japan many older neighbourhoods have narrow streets, which the broadcaster said could have hampered access.