This video grab image obtained November 24, 2020 courtesy of the Utah Department of Public Safety Aero Bureau shows a mysterious metal monolith that was discovered in Utah after public safety officers spotted the object while conducting a routine wildlife mission. Photo: VCG

A mysterious monolith - similar to ones that have appeared briefly in the Utah desert, on a heath in the Netherlands, in Warsaw and on a Romanian hilltop - has now popped up in Toronto.

Canadian media said the four-meter tall shiny metal structure, which appeared to be hollow, was spotted on the city's shore on New Year's Eve. 

Similar ones were also recently reported in Vancouver and in the midwestern city of Winnipeg.

Images posted on social media describing it as "Mono-terrific" showed Toronto's downtown including the iconic CN Tower in the distance. 

Local residents were giddy, eager to get a glimpse of the installation that some suggested online was either "rogue art," left by aliens, or a promotion for an upcoming film.

Others worried that crowds would flock to the Humber Bay Shores neighborhood in breach of public health officials' pleas to stay home during a government-ordered lockdown to slow the spread of the COVID-19 illness.

Nobody has claimed credit for the monoliths that have popped up around the world, and then disappeared.

By Friday morning, the Toronto monolith had already been vandalized with swathes of red paint.

News of the first monolith in the Utah desert in November gained worldwide headlines, with many noting the object's similarity with alien monoliths that trigger huge leaps in human progress in Stanley Kubrick's classic sci-fi 2001: A Space Odyssey.