THE lights will go off in the Brisbane CBD today in a power shutdown of a magnitude not seen since the 1974 floods.

The city's massive power grid will be shut down from 7am, sending 100,000 homes and businesses into darkness.

The drastic measure means virtually every CBD business or home will be powerless.

Power provider Energex has decided to play it safe and before a rising Brisbane River peaks again this afternoon.

It fears a serious health risk would follow if its underground substations, many near the river, are inundated.

About 12 high-power substations that normally each surge with 110,000 volts will be turned off.

Energex crews intend to inspect the sub-stations after the afternoon’s peak high tide to assess the amount of damage and to determine the re-energisation timetable.

Ipswich CBD and inner-city suburbs will also be shut down from 11pm last night.

There are currently 22,000 southeast Queensland properties without power.

There are also thousands more in flooded areas just outside the southeast, including Toowoomba.

Energex spokesman Mike Swanston said safety was the key issue and thanked residents for their patience while repair crews toiled in trying conditions.

"No one should never underestimate the old adage that power and water don't mix, and as water continues to rise Energex will be taking a safety first approach under these extreme weather conditions," Mr Swanston said.

"Similarly, as the weather worsens overnight, power interruptions caused by winds blowing tree branches onto powerlines and other extreme conditions are expected to continue.

"But we ask customers to remain patient as our crews work around the clock in the in heavy rains and high winds."

Mr Swanston urged people with medical conditions that rely on electrical-powered equipment, as well as refrigerated medications, to keep in close contact with their medical practitioner and seek advice.

Mr Swanston added that people who see damaged or threatened power infrastructure should stay well clear and call Energex's priority line on 13 19 62.

He also urged the public to keep out of flood waters near any electrical equipment and stay away from fallen powerlines.

Originally published as Brisbane switches power off