GATLINBURG, Tenn. (WVLT) -- Tickets are flying out the door for this year's Elkmont Firefly Viewing. The annual event has grown so popular over the past few years that the National Park Service decided to start selling reservations.

The reservations come in the form of $1.50 parking passes at the Sugarlands Visitor Center parking lot that are required for every vehicle, with a maximum of six people per vehicle, and are available by clicking the link below or by calling 1-877-444-6777. They went on sale on Monday for the nine-day spectacle, which runs from June 2nd through June 10th.

Three days have already sold out.

Mandatory shuttle buses will take visitors from the visitor center to Elkmont to watch the fireflies at 7:00 p.m. Visitors will have to pay $1.00 round-trip to ride the shuttle.

According to the Park Service, more than 7,000 visitors showed up last year. As the popularity grew, watchers started to show up earlier and earlier, to the point that some of them were arriving as early as 2:00 p.m. to ensure they would get a spot on the shuttle.

The Park Service said some visitors who had traveled from long distances had to be turned away because the parking lot was full and visitors could not get into the visitor center.

It hopes the new system will provide visitors with parking passes that guarantee they will be able to park at Sugarlands Visitor Center, without having to arrive hours in advance.