A highly radioactive substance, emitting in some places radiation 100 times the permitted amount, has been discovered in Switzerland, local media reported Sunday, adding that authorities had covered it up for 18 months.

Swiss weeklies Le Matin Dimanche and SonntagsZeitung reported that federal, regional and local officials decided not to reveal the fact that they had found radium deposits in an old dump in the town of Bienne so as not to scare the 50,000 local inhabitants.

"120 kilogrammes of radioactive waste was obtained after sorting. We measured doses of several hundred microsieverts at the source," Daniel Dauwalder, a spokesman for the Swiss federal office for public health (OFSP), told Le Matin Dimanche.

In certain places, measurements of 300 microsieverts per hour were taken, more than 100 times the permitted amount for an old dump, the newspapers reported.

Exposure for three hours to that level of radiation would be equivalent to the tolerable level over a whole year.

The waste came from a paint used by the watch-making industry to illuminate the numbers on watch faces.

The substance, which has been banned since 1963 due to its radioactive nature, was discovered when roadworks were started at the site.

The OFSP judged the risk to public health "weak", although SonntagsZeitung said that tests on the water table would begin next month.

Public health authorities have shifted the blame back and forth, with local officials saying the OFSP should have informed the public about the incident, and the OFSP saying the responsibility lay with municipal authorities.

The president of the federal commission in charge of monitoring radiation (CPR), which was not informed of the incident, said the various authorities had made a "mistake".

"This will all come back to bite us and it is much more difficult to stay credible and win back the public's trust," Francois Bochud told Le Matin Dimanche.