BOSTON — Massachusetts sports fans raced to their cellphones Friday to begin placing bets as the state allowed online sports wagering just days ahead of next week’s start of the NCAA basketball tournaments.

The start of online sports gambling came a little over a month after the state began allowing people to place wagers in person at the state’s three casinos – Encore Boston Harbor, Plainridge Park Casino and MGM Springfield.

Lawmakers estimate that sports betting could generate about $60 million in annual tax revenue and $70 million to $80 million in initial licensing fees, which must be renewed every five years. The law includes a 15% tax on in-person wagering and a 20% tax on mobile wagering.

People must be 21 or older to bet.

Maine legalized sports betting last year, but the head of the state Gambling Control Unit, Milt Champion, said in January that he doesn’t expect wagering to begin in Maine until early in 2024. State officials are still working on rules that will govern how betting works in the state.

Among those who began betting online Friday in Massachusetts was Taylor Foehl, a 31-year-old graduate student in Boston.

Just after the 10 a.m. start of online wagering, he placed a $5 bet on Purdue to defeat Rutgers in their Big Ten men’s college basketball matchup. He said he picked Purdue because one of his friends joining him at the Cask ’n Flagon sports bar across the street from Fenway Park attended the school.

Foehl said he hadn’t gambled in the past, but that he placed the wager using the FanDuel app “to have a little action on the game” they were watching.

“It’s definitely a good time for it with college basketball reaching their playoffs,” he said. “I’m a big sports fan, particularly of Boston sports. I’ll watch just about every minute of every game when I can.”

Foehl said information about sports wagering has crept into nearly every part of the game.

“It’s hard to learn about sports and consume sports content without hearing about the gambling side of things,” he said.

Richard Bradshaw, a retiree from Worcester, said he was also looking forward to placing online bets.

He said being able to bet directly on college teams could make March Madness office pools “a thing of the past,” but could draw him to teams and sports he might otherwise ignore.

“To watch a game, a meaningless game, now it’s got some meaning if you’ve got $20 on it,” Bradshaw said. “Even golf. I’m watching golf if I’m betting on it.”

At the DraftKings’ Boston headquarters, workers have been gearing up for the kickoff of online sports wagering in the state.

The company was already taking bets in more than 20 states where sports wagering is legal, but the prospect of serving fans of the Boston Red Sox, Boston Celtics, New England Patriots and the surging Boston Bruins is an added thrill, according to company president and co-founder Matt Kalish.

The company is also thrilled that the launch came just before the start of the NCAA basketball tournaments, he said.

“The most common way people jump into the product is usually for some big sports event. It might be the Super Bowl or something upcoming like March Madness,” he said. “So we’re launching in Massachusetts just in time for what should be an amazing tournament.”

Gambling addiction workers have also been preparing for the arrival of sports betting.

Marlene Warner, CEO of the nonprofit Massachusetts Council on Gaming and Health, has cautioned that one demographic the group is expecting to see are young men, which she said are also one of the hardest groups to reach with help for problem gambling.

She warned that young men are both the primary audience for sports wagering and some of those most at risk of gambling at harmful levels.

Kalish said DraftKings monitors for potential compulsive gambling behavior and gives those using the app the option of setting limits on how much they can bet and how much time they spend on the site.

The U.S. Supreme Court in 2018 ruled that banning sports betting was unconstitutional.

Former Republican Gov. Charlie Baker signed the bill legalizing sports betting. Baker, who is now president of the NCAA, argued that residents were traveling to Rhode Island, New Hampshire, New York and Connecticut to wager.

Representatives of professional athletes are asking officials in Massachusetts to toughen regulations to protect players and their families from being threatened by those wagering on games.