The NSW coalition has rolled hundreds of millions more in spending pledges for health services on the 2015 campaign trail.

The NSW government has promised $400 million for a key Sydney hospital, along with thousands more doctors and nurses for others around the state, if it's returned to office on March 28.

Premier Mike Baird committed funding for the second stage of development at Blacktown-Mount Druitt Hospital at a campaign rally for western Sydney MPs in Parramatta on Tuesday afternoon.

"We know the pressures that we're seeing - a population that grows requires the infrastructure to go with it, it's not just the rail and roads we're delivering, it's also the hospitals and schools," Mr Baird said.

"Four hundred million dollars will make a big difference, and we're very proud to be delivering it should we be given the opportunity at the end of March."

The coalition is also promising 3500 extra frontline health positions, including 2100 nurses and 700 doctors.

But neither the premier nor Health Minister Jillian Skinner could say how much the staff boost would cost.

"It's part of the growing health recurrent budget. I think that the total employee-related cost budget accounts for some 70 per cent of the recurrent budget but I haven't done a cost analysis of how much the extra 3500 (would be)," Ms Skinner told reporters.

She said overall costs would depend on the seniority of staff hired.