Gunmen in Nigeria's southern oil city Port Harcourt have kidnapped a senior journalist working for a private national newspaper, police and the daily announced on Monday. 

Donu Kogbara, a renowned columnist for Vanguard newspaper, was abducted Sunday morning from outside her residence in the southern city, which is capital of Rivers State, the daily said.

Gunmen suspected to be gang members shot dead five local residents at the weekend near Nigeria's oil city of Port Harcourt, the police said on Monday.

Rivers state police spokesman Ahmad Mohammed said assailants on motorbikes opened fire on Sunday in the Agbonchia Eleme area, near the country's largest oil refinery.

An explosion rocked an area of the Nigerian oil hub city of Port Harcourt on Thursday, a military spokesman said, but the cause and extent of damage remained unclear.

"There was actually an explosion around Rumuokoro area of Port Harcourt," Lieutenant Colonel Onyema Nwachukwu said of the city in southern Nigeria that is home to a number of oil firm offices.