Indian officials are investigating whether cyberattacks from China could have been behind a blackout in Mumbai last year. State officials in Maharashtra, of which Mumbai is the capital, said Monday that an initial investigation by its cyber department found evidence that China could have been behind a power outage that left millions without power in October. It was the worst blackout in decades in India’s financial capital, stopping  trains and prompting hospitals to switch to diesel powered generators. The megacity has long prided itself on being one of the few cities in India with uninterrupted power supply even as most of the country struggles with regular blackouts.

Anil Deshmukh, home minister of the state, said officials were investigating a possible connection between the blackout and a surge in cyberattacks on the servers of the state power utilities. He wouldn’t single out China, but said investigators had found evidence of more than a dozen Trojan horse attacks as well as suspicious data transfers into the servers of state power companies.

There were attempts to login to our servers from foreign land,” said Mr. Deshmukh. “We will investigate further.”

Another state official said 8GB of unaccounted for data slipped into power company servers from China and four other countries between June and October. The official cited thousands of attempts by blacklisted IP addresses to access the servers.

State-sponsored hackers increasingly target critical infrastructure such as power grids instead of specific institutions, said Amit Dubey, a cybersecurity expert at Root64 Foundation, which conducts cybercrime investigations.

“Anything and everything is dependent on power,” Mr. Dubey said. Targeting power supply, he said, can “take down hundreds of plants or day-to-day services like trains.”

A woman used her mobile phone to light her kitchen in Mumbai during a power outage in October that Indian officials believe may have been caused by China.

PHOTO: NIHARIKA KULKARNI/REUTERS

India’s announcement came after U.S. cybersecurity firm Recorded Future on Sunday published a report outlining what it said were attacks from close to a China-linked group it identified as RedEcho. It cited a surge in attacks targeting India’s power infrastructure.

The report said the attacks could have been a reaction to the jump in border tension between the two countries. During a military skirmish in June, India said 20 Indian soldiers were killed and China said four Chinese soldiers were killed when soldiers fought with rocks, batons and clubs wrapped in barbed wire.

In response to the Recorded Future report, which was earlier reported by the New York Times, China said it doesn’t support cyberattacks.

“It is highly irresponsible to accuse a particular party when there is no sufficient evidence around,” Wang Wenbin, spokesman for China’s Ministry of Foreign Affairs said in a briefing Monday. “China is firmly opposed to such irresponsible and ill-intentioned practice.