23,000 Brisbane homes to flood

A second evacuation centre has opened in Brisbane, with the council revising up the number of homes expected to be hit by record floods to 23,000.

The centre at QEII Stadium on Kessells Road at Nathan, in the city's south, will operate in addition to the RNA Showgrounds at Bowen Hills.

Lord Mayor Campbell Newman said more than 6500 residents are expected to need the centres because they don't have family or friends to stay with.

At 10am (AEST), Brisbane City Council would consider whether a third and possibly fourth centre were needed.

"I don't want to be in a position where we can't look after evacuees who turn up on our doorsteps," Mr Newman told ABC Radio on Wednesday.

The council on Wednesday morning revised upward the number of residential properties that would be flooded to 19,700, and a further 3500 commercial blocks.

Under the new modelling, 2100 Brisbane streets will be flood-hit.

The Brisbane River was at three metres on the high tide at 3am (AEST) and is expected to reach above 1974 flood levels to five metres on Thursday, the Bureau of Meteorology says.

Many CBD businesses have been forced to shut down on Wednesday with energy suppliers cutting power to about 100,000 city customers from 8.30am (AEST).

People had to make their own decision about whether they were needed at work on Wednesday, Mr Newman told ABC Radio.

"It's about whether your job's going to be vital to keeping the wheels of this city turning," he said.

"If you're doing something that means the supermarket shelves are stacked or the petrol stations get supplied with fuel, please, we need you."

Those who can't go to work and are out of harm's way should consider volunteering at sandbagging stations or helping flood-hit residents move their possessions to higher ground, the lord mayor said.

Residents fleeing to evacuation centres are asked to take pillows and sheets, medication, important documents such as insurance papers and spare clothing.