Fans of home team AS Vita, who were losing 1-0 to TP Mazembe, started throwing stones onto the field, prompting police to fire teargas into the crowd.
The teargas caused immediate panic, as tens of thousands of fans tried to leave the stadium. Ten people sustained injuries.
"Waiting for more news from DR Congo too after tragic reports," FIFA president Sepp Blatter tweeted. "My thoughts are with all those who saw loved ones go to a game, not to return."
According to The Independentt, the stadium seats 30,000 people, though stands appeared to be overcrowded.
In a statement, Issa Hayatou, president of the Confederation of African Football, expressed is "deepest sympathy" to the families of the victims.
"Personally, and on behalf of the members of the African football community, I should be grateful if you could extend our deepest condolences to their families, friends and loved ones," he said.
"Further, we wish those that have been reported injured and receiving medical assistance a full recovery."