NSW Premier Gladys Berejiklian is promising billions of dollars more for transport, hospitals and schools as the centrepiece of her re-election pitch, including a $2 billion promise for a rail link to the state's second airport in Western Sydney.

Ms Berejiklian emphasised her government's economic credentials - a growing economy, a record low unemployment rate and a budget surplus - as Prime Minister Scott Morrison watched on during the Sunday NSW Liberal Election Rally launch in western Sydney.