Shares in auto giant Volkswagen continued to slide on Monday, shedding nearly seven percent as the scandal over rigged pollution tests shows no signs of abating.

In late morning trade on the Frankfurt stock exchange, VW shares -- which took a battering last week after the company admitted to installing emission-test cheating devices in its diesel engines -- plunged 6.9 percent to an intraday low of 99.85 euros.

According to German media reports at the weekend, Volkswagen ignored warnings from staff and a supplier years ago that the emission test rigging software -- which sparked the company's worst ever scandal -- was illegal.
German authorities meanwhile heaped pressure on the embattled corporate titan, demanding it set out a timeline by October 7 on how it will ensure its diesel cars meet national emission standards without using the cheat technology.

VW sparked global outrage when it admitted that 11 million of its diesel cars are fitted with so-called defeat devices that activate pollution controls during tests but covertly turn them off when the car is on the road.

The spiralling scandal has badly tarnished VW's name, left it exposed to up to 18 billion dollars (16 billion euros) in US fines, and wiped out a third off its stock market value in a week.

Last Friday, the VW board tapped company insider Matthias Mueller -- chief of its luxury sports car brand Porsche -- to steer the world's largest automaker out of the wreckage.