Eight people were killed in a major fire in the scientific town of Fryazino 25 kilometers (16 miles) northeast of Moscow, the Russian Emergency Ministry said on Tuesday.
"Two people died by jumping out of the window to escape the fire. Six of them stayed inside, collapses occurred there. Preliminary, they are all dead," it said.
Later, the ministry reported that the bodies of four people were found while clearing the rubble.
The fire broke out Monday night in an industrial zone engaged in electronics production. Firefighters rescued one person, but nine more were reportedly trapped inside an administrative building housing offices for about 50 companies, the ministry said.
There was an explosion during the incident, according to preliminary data, a gas balloon blasted.
The fire engulfed three floors and covered a total area of over 5,000 square meters (53,820 square feet), threatening to consume the entire building.
More than 135 people, 55 pieces of equipment, and two helicopters were involved in extinguishing the fire. Sixteen ambulance crews were working at the site.
An emergency operation of the power grid was identified as a preliminary cause of the fire. Investigators have opened a criminal case following the incident.