Electricity North West said the outage is affecting a total of 994 homes in the PR6 and PR7 areas, including Brinscall, Withnell and Wheelton.
Power went off at around 6.50am after an “unexpected incident” on a high voltage cable, with 2,000 homes initially affected.
Engineers are on site and 1,000 homes have since had their power restored.
Electricity North West said the remaining 1,000 homes should have their power restored by 9.50am.
Earlier, a spokesman for the electricity company said: "We're aware of a large power cut in Chorley in the PR6 and PR5 area affecting 2,000 customers.
"This power cut has been caused by an unexpected incident on the high voltage cable that provides electricity to homes and businesses.
"With high voltage power cuts, we're often able to get many of the homes involved back on before our estimated time of restoration.”