The headquarters of German carmaker Volkswagen were being searched by explosive disposal experts on Friday after construction workers found signs of potentially unexploded bombs dating from the Second World War.

Construction workers last month found metal pieces at four locations at Volkswagen's (VW) massive plant in Wolfsburg, a spokeswoman for the city administration said.

Should unexploded bombs be found by the expert squad from Lower Saxony, the western German state where Wolfsburg is located, officials would on Sunday evacuate the 700 or so residents from the Sandkamp district by the VW plant, she said.

Results of the investigations should be known by Friday evening, she said.

Many undetonated World War Two era bombs have been found on the VW factory premises over the years, but modern technology has made deactivating and removing them much easier.

The Wolfsburg car factory employs about 60,000 people in a town of about 125,000. Covering an area three times the size of Monaco, the plant built 815,000 cars last year.

A VW spokesman played down the impact of a possible evacuation on production, saying VW normally does not run shifts on Sunday and plant operations have been phased down since workers departed for the three-week summer shutdown period on July 1.

"There will be no effects on production," he said. Wolfsburg builds as many as 3,800 Golf, Tiguan and Touran vehicles per day during peak times.

The Wolfsburg factory was built under the Nazi regime in 1938 to assemble the People's Car on Adolf Hitler's orders.

But instead of building the vehicle which later became the VW Beetle, the plant was converted during World War Two to produce jeep-type military vehicles as well as aircraft supplies and to repair warplanes, drawing numerous allied air raids.