And last Wednesday, a farm shop in the Südpark area of parkland was set alight. Andrea Schmidt, who owns the store, told the Rheinische Post she was still hoping that the fire was not started intentionally. “Who does something like that … target a farm store?” the paper quoted her as saying.

The first of the fires took place at a disused paper factory on the harbour at the beginning of last month.

Fire services were called upon another five times in April to quench smaller blazes close by. In many cases rubbish heaps had been set alight.

Last weekend several fires broke out on grounds belonging to the RWE energy company in Essen. Firefighters arrived to find an empty storage facility, situated close to a public works station, engulfed in flames. Electricity in south Düsseldorf had to be switched off as a precaution.

Investigators believe the incidents are linked but are not releasing details of how the blazes were started, in case the information inspires copy-cat attacks.

Experts say arsonists are most likely to be under 25 and male. They are often motivated by hatred or jealousy. And in some cases, firefighters start blazes in order to gain social recognition.

Although the fires have so far claimed no injuries, investigators believe it is only a matter of time before a person is in the wrong place at the wrong time.

In the case of the gazebo fire, where containers of propane gas had been stored, firefighters had to fight hard to prevent the blaze engulfing the surrounding forestland.

Andrea Schmidt is planning to re-open her farm shop in a temporary location on Monday. She estimates the fire caused more than €300,000 worth of damages and is hoping that her insurance company will cover the losses.

The Local/kkf