Traffic delays out of Brisbane's CBD are expected until Monday as Energex emergency crews work around the clock to repair a high-voltage electricity cable that was damaged during roadworks.

A contractor using an underground drill hit the 110,000-volt cable — which was live — on Melbourne Street in South Brisbane on Tuesday night.

Repair works only started this morning, forcing authorities to close the outbound lane of the Victoria Bridge, one of the capital's major thoroughfares.

Energex originally hoped the job would be done by Thursday night, but has conceded the damage is more extensive than first thought.

Mr Donald holds a piece of cable, similar to the one that was struck on Tuesday night. ( ABC News: Talissa Siganto )

Energex spokesman Danny Donald said the contractor ran into trouble when using a tunnel bore to dig horizontally under the road.

"The person that has dug into it has made a substantial mess and certainly created a lot more work than we were hoping for," he said.

"Our crews have done a lot more fault finding along the damaged piece of cable.

"It's caused quite a bit of damage to a very important part of the network.

"As it turns out, we may have to continue working a 24-hour shift up until Monday to repair all damage to the network."

The outbound lane on Victoria Bridge is expected to remain closed during Thursday afternoon peak hour. ( ABC News: Anastasia White )

Traffic will be diverted to William Jolly Bridge via Elizabeth Street, George Street and Roma Street.

Bus lanes on Victoria Bridge will not be affected.

"People are pretty good at keeping their eye on traffic issues these days and it's probably wise just to steer clear of the area."

Heavy work is underway to repair the 110,000-voltage cable. ( ABC News: Liz Pickering )

The cable provides power to the CBD, however, network back-feeds are running so the city does not lose power.

The contractor had struck a live wire with an underground drill, but because of safety mechanisms built into the network, electricity was automatically switched off.

Mr Donald said it was possible the incident caused a small explosion.

"Certainly it could have been a very dangerous situation for the person who struck it," Mr Donald said.

"To put that in perspective, this is the highest-voltage cable that we run in the Brisbane area.

"It is essentially 10 times the size of one of the highest-voltage cables you get in your street."