ABUJA, June 26 (Reuters) - Nigeria's Dangote Refinery is operating normally after a fire at its effluent treatment plant, it said on Wednesday, after videos circulated online of dark plumes of smoke at the 650,000 barrel-per-day facility.

The refinery is located in Lekki, roughly 80 kilometres east of Nigeria's commercial capital Lagos.

Dangote's spokesperson Anthony Chiejina did not provide a reason for the fire at the refinery, which was built at a cost of $20 billion by Africa's richest man Aliko Dangote.

"We have swiftly contained a minor fire incident at our effluent treatment plant (ETP)," Chiejina said.

"There is no cause for alarm as the refinery is operating and there is no recorded injury or body harm to all our staff on duty."

The refinery started production in January and will be the largest in Africa and Europe when it reaches full capacity. It could upend what has been a highly lucrative Europe-to-Africa fuel trade and transform Nigeria into an exporter of fuels.

Dangote has said gasoline deliveries from the refinery were delayed until July. (Reporting by Isaac Anyaogu; Writing by Chijioke Ohuocha; Editing by Sharon Singleton and Jan Harvey)