An emergency warning is in place for a fast-moving grassfire burning 14 kilometres east of Wagga Wagga.

The fire is approximately 400 hectares in size and is currently out-of-control.

Fire crews have been deployed to protect properties, while a water bomber is helping firefighters battle the blaze.

The Rural Fire Service says residents should seek shelter as the time to leave has passed.

Meanwhile, authorities warn of catastrophic fire conditions for parts of New South Wales tomorrow.

A total state-wide fire ban will be imposed in New South Wales from midnight, with temperatures set to soar over 40 degrees.

The Illawarra, Shoalhaven and southern ranges are expecting catastrophic fire danger, along with many other high-risk areas.

The Premier, Barry O'Farrell, warns that Tuesday won't just be another hot day.

"Tomorrow will be perhaps the worst fire danger day this state has ever faced," Mr O'Farrell said.