Parts of central Wellington lost power on Saturday morning when a contractor cut underground electricity lines.
Wellington Electricity Lines says 4500 customers were affected in parts of the central business district and the nearby suburb of Newtown, and traffic lights in the area were not working.
Spokesperson Ryan Auger says a contractor dug into underground cables at the Frederick St substation at about 8.30am.
Power was restored just after midday, and the lines company has started an investigation into the cause.
Mr Auger says the company sympathises with inconvenienced customers but notes that third-party incidents are outside its reasonable control.