A fire in a Romanian hospital killed seven coronavirus patients on Friday, officials said, with the third deadly hospital blaze within a year sparking anger over the country's dilapidated infrastructure.

Flames engulfed the intensive care unit of a hospital for infectious diseases in the city of Constanta on the shore of the Black Sea, according to Interior Minister Lucian Bode.

"Five patients were found dead inside the hospital, while two others died while being transferred to other facilities," he told reports.

Officials had earlier said nine Covid-19 patients had died. 

Some 100 people had to be evacuated, emergency services spokesman Razvan Parconie told AFP.

An AFP photographer at the scene saw several patients, some elderly, being carried out through windows as the flames threatened to spread, and a thick column of smoke escaped from the ground-floor unit.

The cause of the fire is not yet known, Health Minister Attila Cseke said, adding that an investigation had been opened.

Gathered in front of the hospital, victims' relatives accused the authorities of "incompetence".

"History is repeating itself. Nothing has been done to improve conditions in hospitals," a woman, who said her mother was killed in the fire, told local television stations.

Hospital director Stela Halichidis insisted several shortcomings found during January inspections of electrical and heating installations had been corrected.

President Klaus Iohannis in a statement said the country had "failed in its fundamental mission to protect its citizens".

The tragedy comes as daily coronavirus infections surge, hitting an all-time record with 12,000 new cases within 24 hours earlier this week, and the EU member is in dire need of intensive care beds.

Experts estimate less than a third of Romania's 670 hospitals meet fire standards.

In January, five patients died in a fire at a Bucharest hospital, two months after another blaze killed 15 patients at a hospital in Piatra Neamt in the northeast.

In April, three Covid patients also died in a mobile intensive care unit in Bucharest after a malfunction in the oxygen supply system.

After these incidents, authorities announced safety checks in the country's intensive care units.