A measles outbreak in Canada's Ontario province continues to grow, with health officials reporting more than 140 cases on Thursday, making it the most severe outbreak in decades.

Public health officials at the epicentre of Ontario’s measles outbreak near London have flagged four new potential exposure sites, including two area hospitals and a medical centre, and are urging people who may be at risk to contact them.

Ontario is reporting 84 new measles cases over the last two weeks, nearly doubling the province’s total count since an outbreak started in the autumn.

The new cases bring the province’s total this year to 119 that were confirmed in a lab and 23 that are deemed ‘probable’