The Local Government Association of NSW has urged the state government against considering two separate elections, drawing on the results of a survey of 84 mayors.

President Keith Rhoades said the survey showed a slight favour for elections to be held in March 2017 for either 3½- or 4½-year terms for councillors.

The first preference of most of the mayors, he said, was for all councils to go to elections in September 2016 for a four-year term or March 2017 for a 4½-year term.

"Whichever way you look at it, the last preference was for different timing for merging versus non-merging councils," Cr Rhoades said.

Premier Mike Baird has previously said that due to the proposed mergers the council elections would likely need to be moved from September this year to March 2017, although the government would still aim for the earlier date.

In a statement on Monday, however, Local Government Minister Paul Toole said that councils not proposed for a merger should plan for local government elections in September.

"If newly created councils are not ready for the scheduled election date, it is intended that the process will be complete in time for them to hold elections in March 2017," the minister said.

City of Sydney councillor Linda Scott said it was critical that only one election was held, as two could cause confusion.

"There's such uncertainty about whether elections will be in September this year or March next year, but the critical issue is that local government elections happen together," Cr Scott said.

"We would have a situation where people on one side of the street are voting in September and the other side of the street in March."

Public inquiries into the 25 proposed Sydney councils, down from 43, are expected to be finished by the end of February. The Boundaries Commission will review the inquiries, with new councils expected to be proclaimed by about the middle of the year.