Ash and dust particles from the massive forest fires ravaging western Canada for the past month have been found in Switzerland, according to Swiss meteorologists. 

"The fires have injected an enormous quantity of dust into the atmosphere, (which) is now being detected over Switzerland," the Swiss meteorological authorities said in a report discreetly issued on Tuesday and picked up by Swiss media Friday.

MeteoSwiss said it had determined that particles observed at the Payerne measurement station in the western canton of Vaud on May 24 and 25 had been emitted from western Canada around May 19-20.

The concentrations measured over Switzerland did not constitute a health risk, it stressed.

The wildfires, which forced the evacuation on May 3 of about 100,000 residents of Fort McMurray and surrounding areas in Alberta province, remains out of control.

But the fires have moved away from populated areas and tracked eastward, allowing Fort McMurray's residents to gradually return to the city.