Hunter Business Chamber chief executive Peter Shinnick told the Newcastle Herald yesterday that businesses would discuss ways to encourage investment in the CBD at the forum on September 24.

He said the GPT decision had led to "a fundamental revision of the way we all conceived the CBD would be developed".

"We're prepared to look at any option that could lead to development within the city," Mr Shinnick said.

The forum will involve delegations from the city's planning, retail, accommodation, hospitality, transport, engineering, legal, financial, government and construction sectors.

Topics on the table will include looking at what planning instruments and physical changes would be needed to encourage further investment in the CBD.

The GPT Group would be invited, but their development plan is considered dead, Mr Shinnick said.

"In the long term, 15 years, 20 years, another GPT may come along," he said.

Some ideas that could be on the table include focusing on increased commercial or residential development in the city centre, and moving the retail precinct towards the west end of the city.

Property Council Hunter director Kristen Keegan said everyone involved in the city was given a huge shake when GPT announced it was pulling out.

"I guess that's a strong lesson for any state government," Ms Keegan said.

"If they want to attract investment, they need to promote certainty."

Local, state and federal politicians will be invited to the forum. Mr Shinnick said the forum would be very different from the meeting hosted by Minister for the Hunter Jodi McKay last Friday.

"The forum last Friday was never ever designed to come up with solutions," he said.

"What we're doing is saying 'let's get together' and work out what we want to contribute to the discussion."