An underground fire in a cable tunnel in Johannesburg has been extinguished but power to the affected southern central business district was yet to be restored, a spokesperson said on Monday.

"The fire was extinguished around 11.30am. We are busy reconfiguration our network to redistribute power from other sub-stations," said City Power spokesman Louis Pieterse.

"We are hoping to have some power restored from 3pm onwards."

The fire has left "everything south of President and Market streets without power", he said earlier.

Pieterse said the cause of the fire was not immediately known.

"It will take a few days to get everything back to normal and the power fully restored," he said.

Sapa