A consortium behind a 300km/h train in China wants to make Sydney its next stop.
Its plan is to run a 200km line from Campbelltown to Newcastle at a cost of about $25 billion.
"Newcastle to Central will be about 40-45 minutes," Centurion Group chief executive officer Patrick Yu said.
The developers say the project could be done without any cost to taxpayers but there is a catch.
The $25 billion would be raised through a levy on new developments along the route while homeowners who sell along the route could be forced to pay a tax of around $75,000.
"If they don't sell their homes they won't pay the levy - it's only when they sell it," Mr Yu said.
Key to the plan is re-designing the Harbour tunnel for the City Metro.
The current plan has two six-metre tunnels but if that was changed to a 16m double-deck tunnel it could take both the metro and high speed trains.
"Yes, it will cost more but we are prepared to discuss paying the difference," Mr Yu said.
Transport for New South Wales has already ruled out the plan.
It says bigger tunnels further under ground would defeat the purpose of an express metro but the government is looking at high speed rail connecting Badgerys Creek, and derailing any high speed plans for Newcastle.