BARRIE, ONT. -- Ontario's much-anticipated COVID-19 vaccine booking portal launched Monday morning for those ages 80 and older, with thousands of people logging on within minutes.

The system estimated a wait time of upwards of an hour within five minutes after its launch.

The Grey-Bruce Health Unit (GBHU) says the backlog has resulted in a domino-effect.

In a statement issued on Monday, the GBHU wrote the provincial phone system's default sends individuals to the health unit to book appointments. "However, the provincial system is not set up to allow the Grey Bruce Health Unit to make appointments, and the resulting calls are overwhelming our phone system."

The health unit also said not to call the Simcoe Muskoka 211 helpline because it doesn't have vaccination information for Grey Bruce.

The GBHU said other health units were experiencing similar issues.

The Simcoe Muskoka District Health Unit (SMDHU) posted to social media, "We understand your frustration and would appreciate your patience as the province works to resolve issues with the COVID-19 booking system."

The post continued, "Our phone line staff and IT department are unable to assist you with these complaints."

The SMDHU said the province hadn't inputted all the region's clinic locations in the system. The health unit added the province was troubleshooting and hoped to resolve the issue by the end of the day.

Premier Doug Ford urged those who don't qualify to be vaccinated to keep off the website, so it doesn't crash.

In addition to booking the shot, the portal guides individuals on scheduling appointments based on each health unit's protocols.

With files from The Canadian Press