Officials in Limburg are trying to find the cause of mysterious spots on hundreds of cars parked close to the A2 motorway in Born.

The damage at first appeared to have been caused by small stones but the black fragments – some form of organic material – are not now thought to be connected, broadcaster Nos says on Friday.

The cars are parked on an industrial zone close to the A2 motorway nearby the Nedcar car plant. New cars which have come off the production line and are awaiting shipment in another car park close by have not been damaged, fire brigade officials said.

Nearby chemicals plant Sabic has not had any leaks and the KNMI weather bureau says there are no reports of any volcanic ash or Sahara sand in the region, which could have caused the damage.

According to local broadcaster L1, the damage could total hundreds of thousands of euros.

Photographs of a black car with considerable paint damage close to its handle and circulating on the internet are not from the Born incident.