(Adds details of the event)
By Kate Abnett
BRUSSELS, April 1 (Reuters) - Police used teargas and water cannons on Thursday to disperse thousands of young people gathered in a Brussels park for a party in defiance of Belgium's COVID-19 lockdown, an event that began as an April Fool's joke on Facebook.
Around 2,000 people showed up towards the end of a warm and sunny day to attend "La Boum" (the party) in the Bois de la Cambre park, local police said, even though the organisers had revealed days earlier that their invitation on social media was a hoax. Local media put the number of people at about 5,000.
Hundreds of police, many in riot gear and some on horseback, broke up a knot of would-be revellers beside a lake in the park with back-up from water cannon trucks and tear gas.
Many in the crowd pumped their fists and chanted "freedom" and some threw bottles and stones at the water cannon trucks.
"We are all depressed. I'll be 18 in two weeks, we want to take advantage of our youth," high school student Amelie, who had come for the party, told Reuters. "We came not to annoy the police, but to show that we also have a life and want to enjoy it."
Reuters reporters at the scene said at least two civilians were injured in clashes, including one woman who was knocked over by a police horse. A police spokeswoman said three policemen were injured and four people were arrested.
The announcement for the party, posted on Facebook in March, promised a host of DJs, singer and producer Calvin Harris and a one-off reunion of French band Daft Punk in the Belgian capital's largest park.
Belgium entered a third COVID-19 lockdown last weekend, with groups limited to four people meeting outside, but this week's sunny weather had already brought thousands out to the park.
The faux party sent police and prosecutors scrambling after nearly 20,000 people said they planned to attend.
Brussels prosecutors have started an investigation to see who is behind the Facebook post.
Brussels Mayor Philippe Close said he understood people need to get some fresh air, but such gatherings would not be tolerated.
"We evacuated the wood. Those who do not obey police risk arrest and prosecution," he said on Twitter. (Reporting by John Chalmers, Clement Rossignol, Kate Abnett, Philip Blenkinsop, Marine Strauss and Bart Biesemans; Editing by John Chalmers, Alex Richardson and Marguerita Choy)
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