Fans gather on day one of Lollapalooza at Grant Park Thursday.
CNN  — 

The start of Chicago’s famed music festival, Lollapalooza, has stirred fears of a rise in Covid-19 cases as thousands gather for four days of performances.

The festival, which kicked off Thursday, is expected to bring hundreds of thousands of people to Grant Park in downtown Chicago. But with nationwide concern over insufficient vaccination rates and the increase of the Delta variant, the event that drew headliners like Miley Cyrus, Tyler, the Creator, Post Malone and Foo Fighters carries new protocols and fears of potential spread this year.

“Folks, #Lollapalooza starts today. We want you to have fun, but please keep all rules and requirements in mind and continue to #ProtectChicago,” Chicago Mayor Lori Lightfoot tweeted.

The Chicago Department of Public Health added nine more states and one territory – Alabama, Alaska, Arizona, Kansas, Mississippi, Oklahoma, Tennessee, Texas, Wyoming and the Virgin Islands – to the city’s travel advisory ahead of the festival.

The total now stands at 14 states and one territory on the advisory, which recommends that unvaccinated people coming from those states obtain a negative Covid-19 test 72 hours prior to arrival in the city, or quarantine for 10 days upon arrival.

Vacc To Lolla lights can be seen over festivalgoers on the opening day of Lollapalooza.

“I expect that we will pass the 200 (case per day) mark and move into moderate risk probably within the next few days,” CDPH Commissioner Dr. Allison Arwady said Tuesday. “Overall, we do remain at lower risk but we are moving in the wrong direction,” she said.

Event organizers advertised that proof of full vaccination or a negative Covid-19 test results within 72 hours of attending will be required to enter the festival.

“I can’t promise there won’t be any Covid cases associated with Lolla. When you’re having this many folks who are coming through, almost certainly there will be some cases,” Arwady said. “I’m certainly hopeful we won’t see a significant problem.”

In a Twitter post, the event said that more than 90% of attendees showed proof of vaccination and 8% brought a negative Covid-19 test.

“For the 600 of you who showed up without paperwork, we hope to see you tomorrow!” the post said.

Despite rising Covid-19 cases, the city’s top doctor said she still supports the festival moving forward.

“I would not feel comfortable moving forward with Lollapalooza without Covid protocols in place. I don’t think I would feel comfortable if this were an indoor event either. And I frankly don’t think I would feel comfortable if we were sitting in Louisiana right now where Covid cases are looking like they’re looking,” Arwady said.

CNN’s Brad Parks contributed to this report.