Militant attacks in Nigeria's oil-producing south have caused water supplies to be turned off in the country's commercial hub and biggest city, Lagos, the state government said on Tuesday.

The Lagos state ministry of information said in a statement that disruption to public supplies has been caused by "shortage of gas" in pumping stations due to attacks on oil and gas pipelines.

The renewed attacks by militants in the Niger delta region have caused oil output to be cut to 1.4 million barrels per day, down from a budgeted 2.2 million bpd this year.

That has compounded government revenue losses caused by the global slump in oil prices since mid-2014, which weakened the naira currency and led to a shortage of foreign exchange.

Fuel shortages have been widespread across the country for weeks, as importers have been unable to source forex to pay for supplies.

Motorists waiting for hours in queues have not been the only ones affected, with householders and businesses reliant on generators to compensate for already patchy public supply.

Bloomberg reported the attacks had hit electricity production, with just 1,000 megawatts produced Monday, down from nearly 2,000 MW last week, because of the lack of gas.

"For all the plants, there's no gas. We're sitting idle here," Dallas Peavey Jr, chief executive of Nigeria's largest generator Egbin Power Plc, was quoted as saying.

The Lagos Water Corporation (LWC) said it was "currently working relentlessly on an alternative power supply for its waterworks" and hoped the disruption would end "soon".

The LWC says on its website it is the largest water corporation in Africa and provides safe drinking water to more than 12.5 million people in the southwestern state.

Lagos city is home to some 20 million people and needs some 2.5 billion litres (540 million gallons) of water per day. But the state provides only 955 million litres.

As a result, many are forced to rely on private deliveries or boreholes.