The aircraft, a Cessna, had problems on takeoff and tried to return to Charleroi to make an emergency landing but crashed on the side of the runway, airport officials said.
"There was a problem on takeoff and they tried to come back, but unfortunately the plane crashed," said Melissa Milioto, an airport spokeswoman. "Five people were killed."
Firefighters sprayed water on the plane that was reduced to a wreck of twisted metal, with only the tail still visible, TV images showed.
The airport was closed immediately after the crash, which happened just before 10am (local time), and reopened at 4pm after an investigation on the runway was completed.
Ryanair, which is the heaviest user of the airport, said it cancelled four departures and diverted inbound flights due to the accident that happened at the start of the Belgian school half-term holiday, when many families go abroad to ski.
Charleroi airport, also known as Brussels South Charleroi, serves as the country's second international airport after Brussels' Zaventem airport and expects to handle 140,000 passengers over the half-term holiday period.
Airport officials said the five killed were three young children, their mother and grandfather - who was also the pilot of the private aircraft - and were all Belgian nationals.
Belgian Prime Minister Elio Di Rupo offered his condolences to the family of the victims via his official Twitter account.
