Twelve injured people were brought in, nine of whom remain in hospital. "They are all responding well to treatment," he said.
Police in Rivers state, of which Port Harcourt is the capital, earlier gave a toll of four dead and four injured, while Buhari's office said "several" people lost their lives.
Conflicting death tolls are not unusual in Nigeria, although the authorities often issue lower numbers.
Crowds tried to force their way through a locked exit.
"Those from behind were pushing and putting pressure on those in front, leading to some persons falling on the ground and being trampled upon," said journalist Egufe Yafugborhi, of the Vanguard newspaper.
The deaths are the latest on the campaign trail: last Thursday, two people were reported to have died during a crush at a Buhari rally in the northeastern state of Taraba.
On January 21, several people were injured in the northeastern city of Maiduguri when a platform collapsed during a visit by Buhari.
"We are also evolving measures to improve on crowd control at such events."
Nigeria goes to the polls on Saturday to elect a new president and parliament, with Buhari looking for a second, four-year term.
Tensions typically mount between supporters of the two sides before, during and after elections. Already, there are claims of attempts to rig the vote.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)