Hawaiian Electric Co. was working to restore power to homes and businesses around Oahu after the state’s only coal-fired power plant unexpectedly went down Wednesday.

The 180-megawatt plant operated by AES Hawaii, an independent power producer, went out of service, prompting HECO to do targeted emergency outages around 11:23 a.m. to avoid a more widespread outage or damage to the electric system from an imbalance of too much demand versus too little available generation, HECO said in a news release.

The plant has the largest single generating unit on island.

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The outages affected customers in Waialua, Kahuku, Waihee, Kaneohe, the Kapiolani area, downtown Honolulu, Waiakamilo, Moanalua, Halawa, Moanalua and Waipahu. Power to most affected customers was restored shortly before noon, HECO said.

“We apologize for this disruption and thank our customers for their patience. We understand any kind of an outage is disruption and we are working with AES to investigate this issue and bring their generator back into service,” Darren Pai, Hawaiian Electric spokesperson, said in the release.

Hawaiian Telcom’s phone system also had troubles Wednesday morning. The company is working to restore service.