Hordes of runners from around the world are trickling into Boston, ready and excited to push their physical limits on Marathon Monday, as officials monitor potential risks in a “heightened threat environment.”

The Boston Marathon is celebrating its 130th anniversary, with upwards of 30,000 runners slated to take off from Hopkinton and traverse through the eight cities and towns along the 26.2-mile course in pursuit of the Boylston Street finish line.

At the same time, public safety officials at the local, state and federal levels are on alert for any threats that might arise on the route. The war in Iran has put the world’s most iconic marathon in a “heightened threat environment,” according to FBI Boston Special Agent in Charge Ted E. Docks.

Docks urged spectators to be on alert and notify law enforcement if they see anything suspicious along the course. He said that “ongoing geopolitical tensions” are increasing the “potential for directed and inspired threats.”

“At this time, there are no specific or credible threats to the race,” Docks said as officials outlined public safety protocols ahead of Marathon Weekend. “We will continue to be vigilant.”

Signs of the running world’s presence started to pop up on Friday in Back Bay.

Inside the Fairmont Copley hotel, professional and elite marathoners fielded questions from the media. Outside, race-related tents covered large portions of Copley Square Park. Thousands of pedestrians took in scenes from around the finish line.

Sterling Crockett, 50, of Belmont, has spectated the marathon at Mile 20 every year since he and his family moved here in 2012. The six-time marathoner will be racing his first Boston and couldn’t help but smile about the thought of running up Heartbreak Hill in Newton.

Crockett is a member of the Dana-Farber Cancer Institute charity team.

“Cancer is terrible,” Crockett told the Herald at the finish line, “so anytime that you can help in that effort, that’s awesome. I am really happy to support that.”

At the Hynes Convention Center, large lines formed outside the Marathon Expo shortly after doors opened for the weekend at 10 a.m. Inside, runners received their bibs, listened to panels on aspects of marathoning and the race itself and shopped around for swag.

Sydney Champeau, 29, flew into Boston from California, ready to conquer her second marathon. The Greater Boston native, who works as a trauma nurse in a Los Angeles emergency room, is racing for the Brigham Women’s Stepping Strong team.

“It’s really exciting to see the commotion that goes into creating the Boston Marathon,” Champeau told the Herald, “driving around the city yesterday, seeing half of the streets shut down.”

More than 10,000 volunteers, including around 1,000 medical volunteers, will support runners through Hopkinton, Ashland, Framingham, Natick, Wellesley, Newton, Brookline and Boston.

Cohasset resident Linda Fechter is celebrating her 30th anniversary as a member of the Boston Athletic Association’s organizing committee, leading volunteers.

Through Sunday, Fechter works at the expo. On Monday, her tasks include working inside an information tent for the family-and-friends waiting area before handing a medal to the last runner to cross the finish line.

“We joke that it is just a race, but it’s not just a race,” Fechter told the Herald.

“For people, this is what they do after they survive cancer,” she added, “or they have turned a milestone age. There are just stories within stories. That’s what keeps me coming back.”

Public safety officials are urging spectators to use public transit, as getting into and around Boston will be more challenging than usual. Large items such as backpacks and strollers should be left at home, and individuals with these items may be subject to search.

Authorities will have uniformed and undercover officers along the course, and cameras will be active along the Boston portion of the course, with observation points set up around the finish line area in Back Bay to monitor the crowd.

“Starting on Monday, all the way through this summer, it’s going to feel like a nonstop whirlwind of excitement,” Boston Mayor Michelle Wu said. “World Cup, Sail Boston, Boston 25; all kicking off on Monday, Patriots’ Day.”