An overtaxed ventilator exploded and caught fire at a St Petersburg hospital killing five coronavirus patients in an intensive care unit, according to Russian officials.

The blaze was apparently started by a short-circuit in the ventilator and was quickly put out by first responders. One hundred fifty people were evacuated from the hospital and an unknown number of people have been injured,the country’s emergency ministry said.

All the patients who died at St George Hospital had been on ventilators.

“The ventilators are working to their limits. Preliminary indications are that it was overloaded and caught fire, and that was the cause,” a source at St Petersburg emergencies department told the Interfax news agency.

It quotes doctors as saying a short-circuit caused a ventilator “literally to explode” because of the oxygen concentration, and the ward filled with smoke, which suffocated the patients.

There have been regular reports of a shortage of ventilators in Russia, verified by President Vladimir Putin himself last month, the BBC’s Sarah Rainsford reports.

Although production has increased, many old ventilators, made in the 1990’s, are still in use outside of a Moscow.

State investigators have opened a case to determine whether there was criminal negligence – either in the ventilator design and manufacture or in the hospital’s fire precautions.

The emergency services dispatched 105 firefighters and 55 vehicles to the hospital, officials said.

Russia now has the second-highest number of confirmed infections worldwide after the United States. On Tuesday, it reported another 10,899 infections in the past 24 hours, bringing the total to more than 232,000.

The capital, Moscow, is the worst-affected area and has reported more than 5,000 new cases in the past 24 hours.

There are reports that some Russian-made ventilators are in use in the United States but they have been inspected for safety.