The record offer would have delivered professional rates of pay for paramedics and an average 19 per cent pay hike, the state government said.
But it was rejected during mediation with the Health Services Union on Friday morning.
"We are bitterly disappointed the HSU has walked away from this," Health Minister Ryan Park said.
"Our state now faces the real possibility of a collapse of our triple-zero service.
"Make no mistake, this strike action will place lives at risk."
Both sides have taken the case to the NSW Industrial Relations Commission to help resolve the long-running dispute.
The Labor government said its latest offer did what the union desired in lifting local salaries to on par with those in Queensland, based on take-home pay, by 2025.
"This is the largest government pay increase in recent history and will take NSW paramedics from some of the lowest paid to some of the highest paid in the country," Mr Park said.
But in reality, the complex four-year offer did not match base pay for Queensland paramedics and would always leave NSW workers short, the union said.
The government had also used inaccurate Queensland base-pay figures, union secretary Gerard Hayes told more than 700 HSU members in a stop-work meeting on Friday afternoon.
"They do not understand how serious this is," he told members on Friday.
"At the moment, you're the lowest paid and the highest injured."
He claimed the offer on the table would lift trainee paramedic pay by six per cent in January with further lifts in mid-2025 and mid-2026 of two per cent and three per cent respectively.
"We've just moved back into the wages cap," Mr Hayes said, a reference to the former coalition government's scrapped policy of limiting public-sector pay increases.
Opposition leader Mark Speakman said the crisis had been created by Premier Chris Minns because he promised more than he could deliver just to get elected.
"He promised large pay rises to the paramedics and now we can't deliver," Mr Speakman said.
"Paramedics are an incredibly hard working, and important part of our health system, and they have been badly let down by a government that lied to them before the election."
The bitter dispute has plagued the government for more than eight months as paramedics pointed to high salaries offered in the ACT, Queensland and Victoria.
Should a deal not be struck by the end of the year, 2100 paramedics have threatened to allow their professional registrations to lapse on January 1.
That would leave one in three paramedics statewide doing little more than driving ambulances and providing basic first aid, the union said..
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