An unknown person or group of people threatened to hammer 7,000 copper nails into the trees if the “photo mania” did not stop, police reported on Tuesday.

Several posters bearing the threatening message showed up in the same neighbourhood as the cherry blossom trees on Sunday, according to the police.

Copper nails are considered a means for damaging trees, though whether they can actually harm them is disputable.

Rather than a hard threat, “we are examining whether coercion might be appropriate here,” said a police spokesman in Bonn.

There have not yet been any indications of who created or distributed the posters.

Thousands of people across the globe flock to see Bonn’s cherry blossoms bloom around this time of year, according to the city's website.

During a two-week period, it's not uncommon to see tourists armed with selfie sticks and mobile phones fill up in the old town's narrow streets.