With 'La Boum 2' dominating headlines and social media - here's a look at the events that led up to this point.
How did we get here?
The event is the sequel to the fake festival that was organised as an April Fools' joke on 1 April, which drew thousands of people to the Bois de la Cambre and ended in riots, over 20 arrests and dozens of people injured.
Here's the timeline of the past week:
On Monday: Close said the city would take "preventative measures," against the event "but if there is no positive response from the crowds, there will be an intervention of the forces of order."
On Tuesday: The administrator of the 'L'Abîme' Facebook page – which announced the event scheduled for 1 May - was questioned by the police. He is released later in the day.
On the same day, Belgian police reached out to Facebook to find out how to stop the spread of the event's announcement. Facebook replied that it would only act if requested to do so by the public prosecutor.
On Wednesday: The Facebook page admin told local media that he is "not organising anything at all."
According to reports, the police suspected the man of setting up a private militia and inciting violence, but that is not true, the man said in a telephone interview with Het Laatste Nieuws.
He says people who decide to join on Saturday are not endangering anyone by meeting outside in a park, referring to several studies – which were also shared by official health authorities – showing that the risk of infection in the open air is a lot lower.
On Thursday: Facebook blocked the event page "in consultation with the public prosecutor's office," a spokesperson for the social network said.
"Our priority is to keep people safe, both on and off our platforms," the spokesperson said. "The local authorities have informed us that this event page does not comply with current legal requirements for Covid-19."
On Friday: Relevant authorities, issued a joint statement issued stressing the event had not received any authorisation.
"Authorisation has not been given for the "La Boum 2" event announced on social media and which is due to take place in the Bois de la Cambre," the Mayor of the City of Brussels, the Brussels Public Prosecutor's Office and the Brussels Capital Ixelles police zone said in a joint press release.
As such, the official advice is not to attend the event and continue to respect sanitary measures in the country.
Police will intervene if needed, and anyone attending risks a fine or an administrative arrest, the statement adds, echoing comments by Brussels mayor Philippe Close on Monday.
"The Brussels Public Prosecutor's Office would like to remind you that any person fined for not respecting the sanitary measures during this event will be prosecuted in accordance with the criminal policy directives in force," the statement ends.
On Saturday: The police in Brussels announced it has started evacuating crowds from Bois de la Cambre and has deployed its water cannons as the unauthorised "La Boum 2" event taking place in the park on Saturday got out of hand.
