Police, justice ministry officials and the local mayor severely underestimated the risks attached to last year’s viral Facebook party Project X Haren, according to leaked documents.

On Friday the official committee looking into how a party invitation turned into a full-blown riot in a wealthy commuter suburb of Groningen will publish its report.

But documents leaked or published ahead of the presentation show there were serious failings at all levels of officialdom.

In particular, the police were unaware of the power of social media. For too long officials continued to consider the party as a hype, even though locals in the commuter suburb of Groningen were becoming increasingly worried, the documents show.

Street names

It was not until September 19, two days before the party was due to take place, that talks on a serious strategy began, the documents show.

Officials decided not to close off the town or involve riot police at an early stage. Instead the police attempted to confuse the stream of partygoers by removing street names.

In the end, 110 people were arrested for public disorder and violence offences and the bill for damages topped €1m.

Several thousand youngsters turned up in the village of 18,000 people after a girl’s 16th birthday party, announced on Facebook, went viral and became a mass hype.