Tournament organisers had earlier confirmed to AFP that casualties had been recorded without providing further details.
“A crush at the entrance to the Olembe Stadium” caused “half a dozen deaths and dozens have been injured”, reported Cameroon’s state broadcaster CRTV.
Earlier, Africa Cup of Nations organising committee spokesperson Abel Mbengue told AFP: “There was a crush as can happen when there is a stampede. We are waiting for reliable information on the number of casualties in this tragic incident”.
The Confederation of African Football, which runs the continent’s flagship competition, said it was “investigating the situation and trying to get more details on what transpired”.
In a statement online, the organisation said it had sent its secretary general to “visit the supporters in hospital in Yaounde”.
It added it was in “constant communication with Cameroon government and the Local Organizing Committee”.
On the pitch, before news of the incident emerged, Cameroon sealed their place in the last eight of a tournament they are desperate to win.
The Indomitable Lions are now due to play Gambia in the quarter-finals this weekend in Douala.
The Comoros side had qualified for the last 16 in their first-ever appearance at the Cup of Nations.
Previously, overcrowding at football matches has resulted in scores of deaths.
Thousands of fans in the Egyptian capital Cairo in 2015 attempted to enter a stadium to watch a game, triggering panic as police fired tear gas and birdshot and resulting in 19 dead.
In April 2001, 43 people died in a stampede at Johannesburg’s Ellis Park stadium during a game between Orlando Pirates and Kaizer Chiefs.
And in Guatemala in October 1996, 90 people were killed in a crush during a World Cup qualification match between the host nation and Costa Rica at an overpacked stadium.