Due to NSW's current COVID-19 outbreak, the local government elections planned for September 4 have been pushed back three months.

Arrangements for the December 4 vote to take place both in person and via post are set in legislation and require an act of parliament to change.

NSW Electoral Commissioner John Schmidt told a parliamentary inquiry on Wednesday that he was legally obliged to arrange for in-person voting, even if the state's strict stay-at-home orders remain in place.

Should this not occur, the election could be deemed a failure.

Mr Schmidt also said that his agency's electoral systems were too slow to pivot from current plans to a full postal or online vote on short notice.

He wrote to the government in July 2020 requesting council elections were conducted by post and online, but the plan was not supported.

However, the government earlier this week agreed to provide the commission an undetermined amount of additional funding to get its work done - and hire more casual staff - for December 4.

This funding would potentially be in the "tens of millions".

"If I was going to move from a mixed-channel local government election to a full postal, I estimated it would take 12 months," Mr Schmidt said.

"A full postal election also requires significant logistical engagement with providers of the service, the printers, fulfilment, putting the postal packs together, sending them out ... there are limited providers who do that.

"In the absence of legislative change, I am required to offer in-person voting - elections will fail unless I do so. It's too late now to move in December to a full postal vote, it can't be done in that time."

Mr Schmidt also said that any further postponement of the December 4 poll would complicate preparations for the 2023 state election.

However, he admitted this may be required if lockdown continues.

"If I'm unable to open polling places, elections could fail," he said.

"If people are unwilling to turn out, there's no minimum requirement for a number of people to vote at a particular election but ... whether that would be a legitimate election would be a matter for others to consider."

The shift to December 4 was the second postponement for the elections, which were initially scheduled for September 2020 but canned in March that year as the first coronavirus wave took hold in Australia.

Electors will be able to cast their vote electronically for the first time, while in-person pre-polling has been extended to 13 days.

The elections will take place across 125 NSW local government areas.

Australian Associated Press