The organisation moved 23 staff into its headquarters in Regent St, Wollongong, in 1990 but its ranks have since swelled to 269 people.

Today the government will call for expressions of interest for the building of a new SES headquarters, to remain in the Illawarra, between Thirroul and Shellharbour.

Emergency Services Minister Michael Gallacher said the new premises should double the current office space to 4500-5000 square metres, including about 1500 square metres for a state operation and communications centre.

The building needed to be close to major bus stops or train stations with frequent services, Mr Gallacher said.

"Communications requirements are also vital for consideration, and the site must be capable of providing constant power to 30-40 per cent of the building, with back-up generators, dual power and telecommunications feeds," he said.

"It must also have the capacity to install aerials, radio antennae and satellite and microwave dishes on the roof."

NSW SES spokeswoman Stephanie Heard said the organisation had outgrown its present base and several teams had overflowed into offices on Crown Street.

The growth in staff numbers was due to the SES increasing its responsibilities and greater community awareness, which resulted in more volunteers needing training, Ms Heard said.

"Back in 1990 our main roles were responding to floods and storms," she said.

"Now we have so many different areas we take part in, [including] the community first-responder program, primary road-crash rescue unit and vertical rescue.

"We've had increased demand for servicing the community, especially due to the extreme weather events we've had in the last few years."

Minister for the Illawarra Greg Pearce estimated the new headquarters would bring 300 construction jobs.

The shift is not expected to affect the Illawarra South Coast division of the SES.

This was moved into custom-built headquarters on Drummond Street at Coniston in 2006.