Essential Energy regional manager northern Ben Williams said the power network switched itself off after it sensed a problem.

Dubbo customers were the first affected, with 6241 premises losing power about 5.14pm, he said.

Eight minutes later, power was cut to a further 2391 households and businesses at Geurie and Wellington.

"Within 10 minutes of the interruption occurring in parts of Dubbo residents would have seen power come on and go off again as we attempted to restore power," Mr Williams said.

"Once the affected area of the network was identified our crews commenced rerouting the network around the problem area and commenced progressively restoring power to those affected."

He said the Geurie and Wellington customers had their power restored by 5.47pm then 457 in Dubbo at 5.48pm, a further 2861 at 6.33pm, 580 at 6.34pm, 1283 at 6.35pm, 995 at 6.38pm and the remaining 65 at 6.41pm.

The power went off again in Dubbo about 9.26pm while Essential Energy repaired damage to the network which had been caused by the original interruption, Mr Williams said.

The incident prompted Wellington Council to issue an alert after a discharge of partially-treated waste water from the local treatment plant it says was a result of the power failure.

"Wellington Council is warning residents to avoid swimming or other recreational activities in the Macquarie River at the Bushranger Creek junction following a partially-treated waste water discharge incident at the Wellington Waste Water Treatment Plant," Wellington Council acting general manager Karen Roberts said.

"Approximately 20 kilolitres of partially treated waste water was discharged from the treatment plant into the nearby Bushrangers Creek.

"The Environmental Protection Authority, Office of Water and Department of Health were notified of the incident.

"Automatic event notification measures minimised the volume of the discharge to the nearby Bushrangers Creek with the plant being brought back to normal operational procedures within 20 minutes of the power failure at the plant.

Wellington Council continues to work with the EPA to improve emergency response procedures at the Wellington Waste Water Treatment Plant in line with current legislation and to further minimise the environmental impact of the facility."

A map posted on Essential Energy's website on Sunday afternoon showed the extent of the widespread outages while residents took to social media to report where they were and when their power went out.

Some residents reported abnormally large queues at fast food drive-through lanes, presumably as residents feared the power outage would mean they were not able to cook their dinner.

"While power was restored to all customers quickly, the problem has caused quite a bit of damage to the network," Mr Williams said.

He said Essential Energy crews would make further repairs to the damaged bypassed sections of the power network.