Officials launched a probe into ventilators used at some Russian medical facilities on Tuesday after five coronavirus patients, including three attached to the breathing machines, died in a fire at a Saint Petersburg hospital.

Officials said the blaze on the sixth floor of the Saint George hospital appeared to have started when one of the ventilators in its intensive care unit short-circuited.

Health authorities said they would check the hospital's ventilators and those at a Moscow clinic where a fire killed a woman last week.

The head of the Saint Petersburg hospital's intensive care unit, Vladimir Sulima, told reporters that four of the patients had died in the ward and three of them were connected to ventilators.

"The staff did everything they could... We feel guilty towards their relatives," Sulima said.

He said they had received the Russian-made breathing machines in early May, adding that the hospital would not be using them until the probe was over.

Images of aftermath after five die in fire at Russian coronavirus hospital
Images of aftermath after five die in fire at Russian coronavirus hospital AFPTV / Evgeny BOGATOV

Health care officials identified the victims as four men and a woman, the youngest of whom was 59.

The circumstances of the death of the person who was not in intensive care were being clarified, prosecutors said.

Around 150 people were evacuated from the Saint Petersburg clinic, which had been repurposed to treat coronavirus patients.

Saint Petersburg governor Alexander Beglov, citing preliminary information, said a short circuit was believed to have caused the fire.

"A ventilator caught fire," his office said in a statement.

Hospital head Valery Strizheletsky said staff acted quickly and managed to avoid more casualties, including by evacuating 15 patients from intensive care.

"This is a black day for our hospital," he said.

The Saint George hospital had been repurposed to treat coronavirus patients
The Saint George hospital had been repurposed to treat coronavirus patients AFP / Olga MALTSEVA

Windows near the top floor of the hospital were blackened with soot as firefighters worked outside.

"Everyone is shocked by what happened," said Svetlana Stepanova, a pensioner receiving treatment at the hospital.

"A fire in the hospital is a nightmare," she told AFP.

A fire at a Moscow hospital treating coronavirus patients last week killed a woman and forced hundreds of others to evacuate.

Russia's federal service for supervising health care, Roszdravnadzor, said on Tuesday it would be checking the quality and safety of the ventilators after the fires.

A factory controlled by state conglomerate Rostec said its ventilators had been installed at hospitals in Moscow and Saint Petersburg.

A spokeswoman for the maker, the Urals Instrument-making Plant, told AFP she could not confirm if their machines had been involved in the recent fires.

Fires at Russian care facilities are fairly common and often caused by lax safety rules.

On Monday, a fire broke out in a retirement home in the Moscow region, killing nine people aged 66 to 90.

Two more elderly women died in hospital later, officials said on Tuesday, bringing the total death toll to 11. Faulty wiring is believed to be the cause of the blaze at the care home.

Russia reported 10,899 new coronavirus cases on Tuesday, continuing a steady increase of new infections that has seen the country become a global virus hotspot.

Russia's reported mortality rate is much lower compared to other European countries hit hard by the pandemic, with 107 new deaths and 2,116 dead from the coronavirus as of Tuesday.