Ronaldo took his international tally to 49, two more than the previous record set by Pauleta, as Portugal ran rings around the Indomitable Lions in a meeting of two World Cup finalists.
"I don't worry about breaking records, it something that happens naturally, with lots of dedication," the 29-year-old told RTP television.
Cameroon were level at halftime but fell apart in the second half as they conceded four goals in a disastrous 18-minute spell.
Portugal went ahead in the 21st minute when Joao Pereira pulled the ball back from near the byline and found Ronaldo, who shimmied past his marker and fired a low shot past Guy Rolland Ndy Assembe to set a new scoring record.
The hosts did not have it all their own way and Vincent Abubakar levelled two minutes before the break when he was given time to control the ball on his chest and score with a shot on the turn.
The second half began with both teams on the attack and Assembe made an outstanding save to deny Ronaldo from close range just after the hour.
But Cameroon collapsed after a dreadful mistake by Aurelien Chedjou, who sent an attempted pass out of defence straight to Raul Meireles and the midfielder gratefully accepted the gift to put Portugal back in front in the 65th minute.
Fabio Coentrao added another two minutes later after he was set up by Silvestre Varela and, with Cameroon wide open, Edinho snapped up the fourth in the 77th minute after Essembe could only touch Ronaldo's shot straight into his path.
Ronaldo completed the scoring in the 83rd minute, firing in a snap shot from 15 metres after two Cameroon defenders failed to clear the ball.
"We are not going to get euphoric because of a 5-1 win," said Portugal coach Paulo Bento.