Nigeria's 650,000-barrel-per-day Dangote refinery is undergoing test runs for gasoline production, with full operation expected by mid-September, according to a note by industry monitor IIR Energy.

The $20-billion Dangote refinery, built by Africa's richest man, Aliko Dangote, on the outskirts of Lagos, began operations in January after years of delays.

Dangote, which has so far only produced diesel and other distillate fuels, had earlier said that gasoline deliveries from the refinery would start in July. Before that the refinery had aimed to start making the motor fuel by May.

It is possible that there could be further extensions, IIR said in a note to clients. Emails to Dangote were not delivered and calls did not connect.

Once fully operational, the refinery is set to upend the Europe-to-Africa fuel trade and reduce Nigeria's reliance on imported refined products.