Young adults make up most of Montreal's new COVID-19 cases with numbers increasing at an exponential rate, according to new information by public health officials.

"Omicron is now representing 90 per cent of new cases," said Montreal public health director Dr. Mylène Drouin Thursday. "We have a positivity rate that is now 18 to 20 per cent."

Drouin made the announcement as part of an update on the epidemiological situation in the city.

"Sixty per cent of new cases are young adults," she noted. "Our wish is to cut transmission before Christmas to avoid the virus spreading to our more vulnerable populations, their parents and grandparents."

With one in five people who get tested receiving a positive result, Drouin admits health officials are struggling to keep up with their contact tracing efforts and cannot continue to follow every case.

"We need you to do some of the work," she said. "If you have symptoms -- fever, sore throat -- we ask you to wear a mask, isolate and get tested, either with a rapid test or in a test centre."

She adds people who have a positive rapid test do not have to get confirmation in a test centre.

"You have to isolate 10 days after you test positive," Drouin said. "Identify your close contacts and ask them to isolate for 10 days also."

Sonia Bélanger, CEO of the CIUSSS du Centre-Sud-de-l'Île-de-Montréal, notes some hospital procedures will be postponed to make room for patients experiencing complications from COVID-19.

"This is a critical time for Montreal's health networks. We are now feeling the impact of rising case numbers on hospitalizations," she said.

Most of the cases in Montreal hospitals are currently due to the Delta variant, but officials say they are ready for potential Omicron-related hospitalizations.

"Know that it is more transmittable and we will have a percentage of severe cases," Drouin said.

Bélanger is also reiterating the government's call for anyone able to help with testing or vaccination efforts to sign up on the Je contribue website in order to speed up the administration of booster shots.

"Please go get your third dose when you are able," she added.

Montreal has been one of the hardest-hit regions in Quebec this fifth wave, with a rate of 515 cases per 100,000 people -- that is, about one in every 200 people.

According to public health officials, the neighbourhoods with the highest number of infections are the Petite-Patrie/Villeray area and the Plateau -- almost one in 100 people reportedly infected.

Other hard-hit neighbourhoods include Hochelaga/Rosemont and Verdun/Saint-Henri/Pointe-Saint-Charles, both of which show rates of over 600 cases per 100,000.