The entire nation of Sri Lanka was left without power on Monday for seven hours after a failure at a key electricity facility.

Power minister Dullas Alahapperuma said an unspecified “technical issue” at the Kerawalapitiya power complex just outside the capital Colombo was the cause of the blackout, which hit the entire nation of 21 million people at about midday.

Power was restored in the capital after seven hours, but some other parts of the island nation were yet to be reconnected.

It was the worst disruption since March 2016, when the whole country was without electricity for more than eight hours following a massive system breakdown.

The public utilities regulator said there would be an inquiry into the failure and gave the state-run electricity monopoly, the Ceylon Electricity Board, three days to explain the disruption.

The power cut caused chaos on already congested roads in Colombo, with traffic lights not operating and police struggling to operate key intersections.

Water supply was also affected because there was no electricity to power the pumps.

Hospitals and other critical infrastructure had back-up power generators. The main airport was already mostly shut because of the coronavirus pandemic.

Sri Lanka generates just over half of its electricity through thermal power. The remainder comes from hydro and wind power.

Kerawalapitiya is an oil-fired thermal power station with a 300-megawatt capacity, equivalent to about 12% of the country’s electricity demand.

Localised power failures are not uncommon but nationwide outages are rare.