Tens of thousands of newly eligible Massachusetts residents eager to use the state’s vaxfinder tool to book COVID-19 shots Thursday encountered a maelstrom of website crashes, system errors, and notices telling them there were many available appointments — but they were out of reach.

The “vax insanity,” as infuriated vaccine hunters dubbed it, dashed the hopes of residents age 65 to 74 and those with two or more chronic health conditions who qualified for the vaccine as of Thursday morning. They thought they could be inoculated soon against a relentless coronavirus that has forced millions into virtual isolation for much of the past year.

“It’s frustrating,” said John Giudice, 68, of Lexington, who likened the experience to being trampled by a mob of baby boomers racing to buy tickets to a Rolling Stones concert. “Everyone is rushing for the door at the same time.”