The steel manufacturing business experienced an electrical blackout about 4.40pm on Monday, after thieves cut the power.

Their actions, cutting through 33,000 volts of electricity, sparked a small grass fire behind the building.

Security staff found an amount of copper wire had been stolen and recovered a burnt hacksaw police believe was blackened after contact with the high-voltage power supply.

‘‘It was an effort to gain entry, so we think more than one person was involved,’’ Lake Illawarra police Sergeant Jason Harrison said.

‘‘The theft occurred during the day, so we think the thieves may have some inside knowledge of the business or conducted some research into when they felt was the best time to go.’’

Sgt Harrison said the culprits may have sustained serious burns, with police keeping an eye out for anyone presenting with burns at Illawarra hospitals.

‘‘It was high voltage, but it would not mean instant death,’’ he said.

‘‘We’re monitoring hospitals, it is highly likely some injury has resulted.’’

Sgt Harrison said police had good working relationships with scrap merchants, meaning any copper taken during the theft would be hard to sell in the Illawarra.

‘‘Not all product taken in the Illawarra is resold here,’’ he said.

‘‘I doubt anything stolen would surface locally, but it may go interstate.’’

He said heavy industrial businesses should secure copper wiring against theft.