Early voting numbers are expected to surge again when pre-polling opens online and at dozens of polling centres across NSW.
Voting for the March 23 state election opened at 8am on Monday, with about 1.5 million people expected to vote before election day.
Australian Political Studies Association vice-president Rodney Smith expected early voting will increase to more than 30 per cent -- up from 25.1 per cent at the 2015 election.
Early voting was just 15.3 per cent in 2011.
"Most of the increase will be in early in-person voting, with a small increase also likely in the iVote," Professor Smith said.
"The main causes in NSW as elsewhere are socio-economic changes which make Saturday voting at a local polling place less convenient than it once was.
"In response, legislators have made it progressively easier to cast an alternative vote, including introducing the iVote in NSW."
iVote was used by about 6 per cent of voters in 2015.
It's available to silent electors, those outside NSW on election day and those with other difficulties voting in person.
About 14.2 per cent of voters in 2015 pre-polled in person while about 5 per cent voted via the post, according to NSW Electoral Commission data.
- Pre-polling day voters register at ivote.nsw.gov.au or 1300 2 iVote.
Australian Associated Press