Scores of asylum-seekers evacuated a large hall on Tuesday in the German city of Düsseldorf after the building caught fire.

Some 130 men who were in the building as the fire broke out have been rescued, a fire department spokesman said.

Around 28 refugees were treated for smoke inhalation, and authorities cautioned locals nearby to keep their windows and doors shut.

Later on Tuesday, Düsseldorf police and the prosecutor's office announced they were investigating six of the hall's residents on suspicion of arson. The men were brought to police headquarters for questioning.

By the time fire engines arrived on the scene, the entire 5,000 square-meter (53,820 square-foot) building was completely engulfed in flames. The cause of the fire remains unknown.

According to city officials, a total of 282 male refugees from Syria, Iraq, Nigeria and Afghanistan were being housed in the former trade show hall, but emergency crews said all who were on site were successfully evacuated from the burning building.

Many of them were asleep when the fire started but were woken up in time by members of the German Red Cross.

North Rhine-Westphalia's interior minister, Ralf Jäger, offered to house the displaced refugees in a state facility, assuring that all the residents will be given a place to stay by the end of Tuesday.

The blaze's towering kilometer-high cloud of black smoke alarmed many nearby, including passengers at Düsseldorf's international airport and the city's large trade fair.

The trade fair complex, which is currently hosting thousands of visitors for a print media exhibition, was also not harmed by the blaze.

Germany has seen over 40 arson attacks this year alone on refugee shelters.

In 2015, Germany took in some 1.1 million people seeking asylum, many of them fleeing conflict, poverty or persecution in the Middle East and Africa.

rs/kms (AFP, dpa, Reuters, epd)