The explosion brought down the gate of the secretariat while doors, windows and other property were destroyed.
This is the second time the Chief Tony Okocha-led APC would be experiencing such an attack at its secretariat this year.
This came as the local government elections is set to hold in the state today as the Rivers State Independent Electoral Commission said on Friday that all sensitive materials have been distributed to the various local government areas.
A viral video of the incident scene seen by our correspondent showed some workers at the facilities going round to ascertain the extent of damage.
When contacted, the spokespetson for the state police command, Grace Iringe-Koko, said she had yet to get a report on it but promised to revert.
The party has yet to make a statement on the incident.