The annual Sturgis Motorcycle Rally kicked off in South Dakota on Friday, with thousands of bikers descending on the streets of the Black Hills region despite warnings from health experts that the event will further fuel surges of the highly contagious delta variant.

The annual gathering, which was labeled a “superspreading event” last year, is expected to attract at least 700,000 people over 10 days, even as just 46 percent of adults in the county that hosts the rally are fully vaccinated against COVID-19, according to the Centers for Disease Control and Prevention (CDC).  

In South Dakota, about 67 percent of adults 18 and older have received at least one dose, with about 60 percent fully vaccinated as of Friday. 

Despite growing concerns on the rise of the delta variant, especially among unvaccinated communities, the city of Sturgis held an opening ceremony Friday for the 81st annual rally. 

The city didn't hold an opening event at last year’s gathering due to COVID-19 concerns. 

The New York Times reported that by midmorning Friday, the city’s Main Street was packed with attendees walking shoulder to shoulder and congregated near dozens of bikes parked outside of businesses. 

The Associated Press reported that city officials this year are allowing rally attendees to drink alcohol on public property to encourage more people to remain outside and to limit the crowds gathered in indoor locations. 

Sturgis’ city manager Dan Ainslie also told the Times on Friday that event organizers were “encouraging people who are in a high-risk category, whether it be age or because of comorbidities, that they come next year.” 

However, the event, which attracts rallygoers from across several U.S. states, has prompted warnings from health experts including from the Minnesota Department of Health, which is advising people of the risks of large gatherings for long periods. 

"The risk increases with larger groups and longer durations of exposure, especially in settings where there may be many unvaccinated people and social distancing and wearing masks aren't routinely practiced," the department said this week, according to the Star Tribune. 

"Any event or setting that is conducive to spreading the virus will continue to allow more variants to develop, undermining the gains we have already made with this virus,” the statement added. 

Last year, the CDC tied at least 86 COVID-19 cases among Minnesota residents, including one death, back to the Sturgis rally, when about 460,000 people attended the motorcycle event. 

A spokesman for South Dakota Gov. Kristi Noem (R) said she planned to attend the motorcycle rally this year after she approved the event, with the AP reporting that she will be participating in a charity ride.