Premier Dominic Perrottet is seeking a fourth term for the coalition, while Labor leader Chris Minns wants to end Labor's 12 years in the political wilderness.
Labor is favoured to secure a tight victory, leading the polls but there is a strong possibility the election could deliver a hung parliament.
With 93 seats up for grabs, whichever side can secure 47 will be able to form a majority 58th NSW government.
The coalition has governed for two years in minority and has 46 seats, while Labor has 38, with nine crossbenchers, including three Greens MPs.
If Labor wins six seats it could govern with support of the the Greens if it agrees to no more coal or gas projects, an end to logging in native forest and mandatory cashless gaming.
The leaders have led the charge on the campaign trail this week, visiting dozens of electorates in a frenzied blitz to shore up seats across the state.
The premier voted in Beecroft on Saturday morning, accompanied by wife Helen and daughter Celeste, as school volunteers sold cupcakes and sausages to punters.
"It's a very important day for the future of our state. There's a lot at stake", Mr Perrottet said.
"It's my team that has the plan to dealt with the current challenges."
Mr Minns voted in his ultra-marginal southern Sydney seat of Kogarah, flanked by wife Anna and their three sons, and promising a fresh vision for the state.
"Vote for a fresh start for NSW, for a team that's got a plan for essential services, for our schools and for our hospitals, who's going to stand up against privatisation and really put the people of NSW first," he said.
Both leaders have campaigned hard in vital seats in Sydney's west, where a third of NSW voters live and many electorates are on a knife edge.
The latest Newspoll showed Labor leading the coalition 54.5 to 45.5 on a two-party preferred basis, putting Labor on a path to claim the 10 seats it needs to form majority government.
Former NSW Labor premier Morris Iemma told the Nine Network he was "cautious but optimistic" about a Labor victory.
Former Labor NSW deputy premier Carmel Tebbutt said Labor had "a mountain to climb" to win.
Earlier on Saturday Prime Minister Anthony Albanese lent his support to Mr Minns' pitch for premier, campaigning in the Liberal-held seat of Ryde before casting his own vote at a booth in Sydney's innerwest.
A string of retiring senior Liberal ministers bailing out before the state election showed the Perrottet government didn't even have confidence in itself, he said.
"It's time for a change of government," he told reporters.
Former NSW Liberal minister Andrew Constance predicted it would be the night of the cross bench.
"We're going to see the largest crossbench I think, elected in the state's history tonight," he told Nine.
A raft of minor party and independent candidates could make the difference in the event of a minority government, with the Greens and teals vowing to hold the government to account on climate and other reforms.
Kingmaker Alex Greenwich, who is looking to win again as an independent in the seat of Sydney, said there had been a trend away from the major parties towards smaller parties and independents.
Sidestepping the question of who he would support in the case of a hung parliament, Mr Greenwich said it would be incumbent on the crossbench to provide the next government with stability.
