Tens of millions of people were affected by the outage which plunged buildings across Jakarta into darkness.

Power has been restored in most parts of Indonesia‘s capital, Jakarta, after the city of 10 million people went without electricity for more than nine hours due to technical issues, according to the state power company.

Sunday’s outage, which also hit neighbouring provinces, spread across an area populated by more than 100 million people and appeared to have affected most of the capital, prompting the use of generators in some offices, malls and apartments.

The blackout began just before noon local time (0500 GMT). The state-owned electricity company, PT Perusahaan Listrik Negara (PLN), said it had been able to switch 17 electrical substations around Jakarta back on by 9pm, but two others were still in the process of being restarted and four remained off.

“The recovery process is still ongoing and indeed it cannot be turned back on at once immediately, but rather gradually we try to normalise with maximum efforts,” Sripeni Inten Cahyani, acting chief executive of PLN, said in a statement.

While the megacity has been hit by blackouts before, Sunday’s shutdown was unusually long.

A traffic light is seen turned off during a power outage in Jakarta, Indonesia [Dita Alangkara/AP]

Earlier in the day, Cahyani blamed faulty transmission circuits on the Ungaran to Pemalang power line in Central Java for causing voltage drops that hit power networks in the capital as well as West Java and Banten provinces.

“We will investigate to find the root causes and analyse them in detail. We will appoint an independent party to investigate,” said Cahyani, who only took up her post on Friday.

Operations at Jakarta’s international airport and public hospitals remained normal, relying on back-up generators.

But at train stations, hundreds of passengers were left stranded after commuter lines stopped working.

“The train stopped all of a sudden, we had to wait for a long time,” said Ella Wasila, a passenger near Sudirman station in downtown Jakarta.

“There were so many babies in the coach, they were crying, and people were shouting ‘open the door’.”

The power outage also disrupted some cellular phone networks and provider Telkomsel said it was compiling an inventory of the number of devices affected by the power cut.

The incident also caused traffic lights to go out in some areas of the capital, creating traffic jams.

The city of Jakarta is the centre for government and business in Indonesia. The capital does suffer periodic blackouts, but they are usually short-lived and confined to certain areas

The Indonesian Consumers Foundation said the blackout could discourage investment in Southeast Asia’s biggest economy and urged the government to increase PLN’s capacity.

“Power outages, especially in the greater Jakarta area, are not only detrimental for residential consumers but also to the business sector,” Tulus Abadi, an executive at the foundation, said in a statement.