COLOMBO, Oct. 18 -- Traffic lights stood dead in Colombo on Saturday and a roadside stall sat with its lights off as Sri Lanka's national grid failed, leaving the state-owned grid operator to ask households with rooftop solar panels to switch them off.

The government's information department put the outage down to system instability, Anadolu Agency reported. Energy Minister Anura Karunathilake said a breakdown at the Upper Kotmale Power Station was suspected of causing it.

The National System Operator, or NSO, later denied reports of power plant breakdowns, according to the same Anadolu report. It said the hydropower plants that were running stayed online to help restore supply, and that the Norochcholai coal plant was shut down under s...