Police on horseback and using a water cannon charged a crowd of thousands of people gathered in a Brussels park on Friday for a fake concert announced on social media as an April Fool's Day prank. AFP journalists at the scene saw at least one police officer injured and several people in the crowd arrested in the Bois de Cambre park on the southern side of the Belgian capital. The police, wearing protective helmets and advancing in a line, moved in to enforce strict Covid-19 social-distancing rules that prohibit gatherings of more than four people outdoors. The crowd responded by throwing projectiles, hitting at least one police officer. Brussels law enforcement authorities on Wednesday had issued a warning that the announcement on social media of a "party" was illegal and that its organisers could be prosecuted. Contacted by AFP, police were not immediately able to give numbers for the size of the crowd, deployment of officers or the number of arrests. Belgium on Saturday imposed tighter restrictions aimed at curbing surging Covid infection numbers. They include closing schools, keeping borders closed, limiting access to non-essential shops and lowering the number of people able to meet outdoors to four. kf-rmb/arp/dl