A big fire broke out in a mental hospital in Russia's Moscow region early Friday, killing at least 38 people, local authorities said.

"We have a list of 38 people who have died and been identified," a source in the hospital told Xinhua through telephone.

Two patients and one nurse escaped the fire unharmed, she added.

The Health Ministry confirmed the death toll, saying 36 patients and two medical workers were killed in the tragedy.

The fire broke out at 2:23 a.m. local time (2223 GMT Thursday) in a single-story wooden building of the Ramenskoye 14th mental hospital in Moscow's northern Dmitrov district. The blaze was brought under control after about four hours.

The fire might have been caused by short circuit in the building, the police said, adding that most of the people died asleep inhaling the fumes.

Since the fire broke out at night, it was hard for those inside the hospital to escape. Search and rescue work was hindered due to the heavy smoke around the building, which was almost burnt down.

According to emergency authorities, fire engines arrived too late and missed the opportunity to put out the fire at the early stage, as the nearest fire station is located 50 km away.

Following the tragedy, Andrei Vorobyov, interim governor of the Moscow region, declared a day of mourning.

President Vladimir Putin ordered authorities to investigate the tragedy and assist the survivors.

The local government on Friday launched a massive fire safety check at all social institutions in the Moscow region, including hospitals and schools.