Six residents of a refugee shelter in the German city of Dusseldorf were arrested on Tuesday on suspicion of deliberately starting a fire which completely destroyed the building, authorities said.
Investigators said that the men had been taken into police custody for questioning.
The accommodation houses around 130 men, all of whom were safely evacuated during the blaze, fire safety officials said. Twenty-eight of the residents were being treated for smoke inhalation.
A fireman and a volunteer at the hall also sustained minor injuries.
Germany has seen a spate of arson attacks and other hate crimes at refugee homes in recent months, as a surge in migrant arrivals fuels anti-foreigner sentiment.
Police are also frequently called out to brawls at migrant accommodation as patience wanes in overcrowded conditions and ethnic tensions among housemates intensify.