Details of the incident are still sketchy but residents around the area say the explosion was a result of a bomb planted in a commercial vehicle.
Two people are said to have died on the spot and several others injured. But that could not be independently verified at this point.
The police in the state could not be reached for comments. No one or group has claimed responsibility for the explosion.
The National Emergency Management Agency has issued a one-paragraph statement confirming the explosion, saying the driver of the commercial bus had been confirmed dead.
"NEMA confirms an explosion today in a commercial bus at Rumuokoro roundabout in Port Harcourt," the statement by the agency's spokesperson, Yushau Shuaibu, said.
"The driver died from the explosion. The situation is under control."
Our reporter who visited the scene said the affected bus broke down and was being pushed off the road by its occupants when the explosion went of.
He said one of the three people pushing the bus died instantly while scores of other people were wounded and rushed to hospital.
The police however claim the victims of the explosion were armed robbers. “Luck ran out of them while going on operation,” the state police commissioner was quoted as saying.
The Rivers State Governor, Rotimi Amaechi, also gave a similar account of the incident while speaking on CHANNELS TV.