PowerNet Ltd chief executive Jason Franklin said the company suspected one pole was struck by a vehicle, which then brought down the other two.
The company’s investigation of the incident would continue today after power was fully restored, he said.
An employee at a nearby business was taking a break outside when they witnessed the poles collapse one after the other into the centre of Mersey St.
Employees of the business said they were inside when they heard a loud bang, followed by a momentary loss of power.
The collapsed poles appeared to have narrowly missed vehicles parked on the opposite side of the industrial street.
No injuries or damage to property were reported.
PowerNet listed the outage as occurring at 3.15pm.
Affected localities included Bond St, Invercargill Inner City, and Mersey St.
Mersey St was closed to traffic while workers undertook repairs.
