Emergency authorities in the German port city of Hamburg responded to multiple calls from residents late Wednesday over a mysterious bad smell that wafted into several districts.

Firefighters with special vehicles made their way to the eastern districts of Uhlenhorst, Eilbek, and Wandsbek after receiving multiple calls after nightfall about an acrid smell.

Authorities told residents to keep windows and doors closed. The fire services were unable to determine the source of the odor and left the scene early Thursday.

The stench, which fire services spokesman described as similar to used oil, dissipated throughout the night hours.

There was no indication of a danger to public health, according to a fire brigade spokesman.

A stench hung over the port city around a week ago. A number of alarm calls were made to the fire services regarding a smell of gas to the north of the River Elbe.

The cause was found some hours later in the port. Emergency services described it as a chemical by-product causing a rotting stench.