RIO DE JANEIRO — A small, unmanned hot-air balloon crashed into the roof of one of the arenas in Rio’s Olympic Park on Monday, causing minor fire and water damage but with no reported injuries.

Rio organizing committee spokesman Mario Andrada said the small balloon — often called a sky lantern or Chinese lantern— was probably launched from one of the city’s favelas and hit the Carioca 3 Arena.

Andrada said “firefighters used a lot of water, and water spilled into the field of play.”

The balloon struck early Monday morning. Officials were able to repair the limited damage, which allowed a wheelchair fencing event to start on time.

Andrada said launching the unmanned balloons is a Rio tradition, often to celebrate church feast days. He said police are investigating who launched the balloon.

Andrada said the balloons are illegal and “particularly dangerous when they fall into big houses or big factories.”