Firefighters continue to tackle a blaze at an electricity sub station on Gwallon Lane in Marazion.
The fire, which involves a transformer at the sub station, broke out just after 10am.
Two fire engines from Penzance were called, along with one each from St Just and Hayle, and initially firefighters worked to prevent the fire from spreading while electrical engineers were sent to isolate the power supply.
Devon and Cornwall Police were also on hand to close nearby roads, due to the volume of smoke.
Just after midday, Cornwall Fire and Rescue Service reported: "The foam response pod from Newquay has been requested and is mobile to the incident along with a further whole time officer."
At around 1.30pm it was reported that crews were still awaiting confirmation from Western Power that the substation had been isolated, and at 3.30pm four major pumps, a support vehicle, the foam unit, four flexible duty officers and the duty area manager were still in attendance and reported to be "remaining defensive."
A spokesperson for Western Power Distribution said 750 customers were without power, which is expected to be restored within the hour. They added: "Engineers are working on the fault now and the fire is out, but firefighters are still in attendance."
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