An aerial view of Johannesburg

Massive areas of South Africa’s largest city were hit by power outages on Friday afternoon after a power line from state-owned utility Eskom tripped during planned maintenance.

At least 20 substations, each servicing at least 10 suburbs, have been affected, said Isaac Mangena, a spokesman for Johannesburg’s City Power. There’s no estimate yet for when power will be restored.

Friday’s blackout is a stark reminder that generation capacity isn’t the only threat to power supply in the economy — much of the country relies on ageing distributing and transmission infrastructure.

The outage comes as Eskom itself is struggling to generate enough power to meet demand and has implemented rolling blackouts on several occasions in recent months.

The company said earlier it might need to implement cuts today, but has confirmed it hasn’t done so yet.

The central and northern suburbs of Johannesburg were particularly affected, including the Sandton CBD.  — Reported by Prinesha Naidoo and Renee Bonorchis, (c) 2019 Bloomberg LP