The fire erupted on the ground floor of a residential building in the Brateyevo District where the hostel was located.
"According to preliminary information, eight people have died," a spokesperson for the emergency services told Sputnik.
The spokesperson added that the victims had died of carbon monoxide poisoning.
According to the spokesperson, the fire was likely caused by an electrical fault.
The high number of fatalities as a result of the fire at the hostel in southeastern Moscow is explained by lattices installed on the windows, an acting head of the city department of the Russian Emergencies Ministry said.
"The main cause of the deaths is the lattices installed on the windows," the acting head said.
He added that there was a fire alarm at the hostel but it did not work.
The Emergencies Ministry said that the fire had been already extinguished. Three people have received medical assistance.