“The immediate danger has passed,” the authorities said in the Nina warning app on Friday. Authorities initially warned of an “extreme danger” to health within a 1,000-metre radius and urged people to remain indoors.

Nitric acid is a highly corrosive industrial chemical that can severely burn the skin, eyes and airways.

An unpleasant odour could still be noticeable across Krefeld, including in the city centre, but the authorities said this did not pose a danger to the public.

A fire service spokesman said they had now managed to pump 13 metric tons of nitric acid from the overturned lorry into another vehicle.

The emergency services had also been able to recover most of the approximately 10 tons of nitric acid that had leaked onto the carriageway using a specialized vacuum truck.

The accident occurred overnight when a lorry carrying 23 tons of nitric acid overturned and was badly damaged, causing the corrosive substance to leak onto the road.

The next step will be to use a crane to right the lorry and remove it from the motorway.