Police in Belgium have used tear gas and water cannon to break up a crowd of people who had gathered for a fake concert that was announced on social media as an April Fools' Day joke.
About 2,000 people attended the event in Brussels' Bois de la Cambre park, in defiance of the country's Covid-19 measures.
When police arrived, on foot and on horseback, some in the crowd shouted "Freedom!" and threw projectiles.
Police said four people were arrested.
Three police officers were injured in clashes, according to officials. Reuters news agency reported that at least two other people were injured.
The announcement for the concert was posted on Facebook in March, promising a host of famous DJs.
Organisers said the invitation was a hoax, but many people still showed up.
"We are all depressed. I'll be 18 in two weeks, we want to take advantage of our youth," one student who attended the gathering told Reuters. "We came not to annoy the police, but to show that we also have a life and want to enjoy it."
Under coronavirus restrictions in Belgium, outdoor gatherings are limited to four people.
Prosecutors say they have started an investigation to find out who was behind the Facebook post.
Brussels Mayor Philippe Close said he could understand people wanting to go outside in the spring weather, but such gatherings would not be tolerated.
Belgium, with a population of 11.5 million, has recorded more than 882,000 coronavirus cases and 23,000 deaths.
It is one of a number of European countries to increase restrictions amid a rise in cases.