The Queensland opposition says the government's "new" plan to solve Brisbane's rail congestion woes is old, and was dismissed years ago because it was too expensive.

The Newman government is planning a multi-billion dollar tunnel under the CBD as an alternative to the defunct Cross River Rail plan, The Courier-Mail reports.

Dubbed the Brisbane Underground, the rail and bus network is in the final stages of planning, the paper says.

The tunnel will join the south side of the river with George Street and include underground stations in the city and it's understood the project will be jointly funded by the state government and the private sector, the paper says.

Premier Campbell Newman on Monday said his government's plan would cost billions less than the former Labor government's $7 billion Cross River Rail.

He would not provide details but said it would solve rail and bus issues in the CBD, and hinted work would start within the next few years.

But Opposition Leader Annastacia Palaszczuk says Mr Newman's plan is an old idea the former Labor government dismissed years ago.

"This was mooted some five or six years ago and it was too expensive for the state government to move ahead with," she told ABC radio on Tuesday.

She said the Cross River Rail project was ready to go, and been ticked off at both the state and federal levels, and would create 7000 jobs.

"It is the solution for the congestion that will happen on our rail network," she said.

"The government today needs to explain what their alternative is, and how long its going to take."

She said if the government was starting again from scratch, any congestion solution would be at least a decade off.

A spokesman for Transport Minister Scott Emerson told AAP it was the former Labor government's plan that was unaffordable.

"It was never affordable."