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Power workers are trying to locate and repair a faulty underground cable.
It left hundreds in Dartford without power this morning.
Fleetdown Primary School in Lunedale Road closed for the day because of uncertainty about the power supply from a replacement generator.
A spokesman for UK Power Networks apologised and said 348 customers lost their power supplies because of the faulty cable. Power was restoired by 9.15am.
"All customers are being powered by temporary generators while full repairs to the cable are undertaken.
"The customers will be restored to the permanent network."
The school will be open in the morning.