A lightning strike on a transmission tower left swathes of Johannesburg without power this afternoon, City Power said.

"It is very widespread," said spokesman Louis Pieterse of the outage which stretches from at least Rosebank in the north east to Mondeor in the south.

Court cases at the Johannesburg High Court, including judgment in the "Jeppestown massacre" case, were among the daily affairs put on hold as technicians tried to repair the damage and restore power.

The strike also caused a conductor to fall onto a truck but, said Pieterse, it did not initially appear that there were injuries.

Power was expected to be restored at about 6.30pm if restoration efforts were successful, he said.

Commuters reported that travelling conditions were difficult in the rainy conditions without traffic lights.

Metro police advised motorists to reduce speed, keep their headlights on and keep a safe following distance.