A deadly fire ravaged a psychiatric hospital in the north of Moscow during the wee hours of Friday morning leaving at least 38 people dead, Russian authorities said.

The blaze started shortly after 2:00 a.m. local time, 22:00 GMT Thursday, and was put out almost three hours later, in a one-story hospital in the town of Ramenye north of Moscow, RIA Novosti news agency reports. A total of 41 people were believed to be in building at the time of the fire.

“According to preliminary reports, 38 people died, including two medical personnel,” Russia’s health ministry spokesman Oleg Salagay told RIA Novosti.

“Three people survived -- a medical nurse led two patients out of the burning building,” Salagay said.

A police source told RIA Novosti that most of the patients died in their sleep inhaling the fumes as they were likely sedated by prescribed medicine.

Regional emergencies services said 12 bodies have been found so far in the building that was almost completely burned down. The search is hampered by heavy clouds of smoke around the site, the report adds.

Vadim Belovoshin, deputy emergencies chief for the Moscow region, told news agencies that firefighters could reach the scene only an hour after receiving a fire alarm notice, because a local ferry across the river was closed and they had to make a detour. He added that the hospital windows had bars, but the building had two fire escapes.

Authorities have launched an investigation and Saturday has been declared a day of mourning.