Police and the fire department have warned people in Hamburg, Germany, to close their windows after a large fire engulfed several warehouses and sent black, chemical-laden smoke drifting over the city.

About 140 people were evacuated on Sunday, and it is not yet clear how dangerous the situation is, a police spokesperson said.

A fire department spokesperson said it had reduced the threat level somewhat even though the fire was still burning at midday (10:00 GMT) but that people should remain indoors with their windows closed.

Authorities said the fire began about 4am (02:00 GMT) in the Rothenburgsort district, located in the eastern part of Germany’s second largest city.

The smoke drifted towards the city centre, halting long-distance trains between Hamburg and Berlin and other cities.

A public safety alert conveyed through a mobile phone app advised people in Hamburg to close windows, turn off ventilation systems and air conditioning, and to avoid the area. No injuries were reported.

Public broadcaster NDR said the fire involved containers of hydrogen sulfide, a toxic and foul-smelling substance, forcing firefighters and police officers in the area to wear breathing apparatuses.

The police spokesperson said the sky had darkened as a result, but the weather made it difficult to determine how much was smoke and how much were clouds.

In July 2021, an explosion at a chemical park in the western German city of Leverkusen killed two people and injured dozens. (Al Jazeera)