NEW YORK (CBSNewYork) — About 50,000 runners took part in the TCS New York City Marathon flanked by crowds of spectators Sunday, and officers were on high alert.

As CBS2’s Raegan Medgie reported, the extra security seen at the marathon will continue due to a pre-Election Day threat from al-Qaeda.

During the marathon, heavily-armed officers with rifles were in place throughout Central Park. K-9 units were seen patrolling the area where the marathon finishes.

Sanitation trucks were also set up, acting as traffic barriers to deter car bombs. And early Sunday morning at the start of the race, snipers were perched on the Verrazano Narrows Bridge.

The purpose was to ensure the safety of the runners, spectators and fellow New Yorkers at a time when the country was on high alert for a possible terror attack on Monday – the day before Election Day.

U.S. intelligence alerted Joint Terrorism Task Forces last week that al-Qeada could be planning attacks in three states on Monday, sources told CBS News.

Officials said the intelligence points to possible attacks in New York, Texas or Virginia.

The threats were vague and no specific targets were provided, but authorities took the threat seriously and ramped up security. Those precautions went for the marathon too.

“At the start of the race, there were police in armor,” said Bob Scheungrab of Gettysburg, Pennsylvania.

Scheungrab was among the runners who hit the pavement that started off a week filled with heightened security.

“Out on the course, every intersection had police there,” Scheungrab said. “There were police cars everywhere.”

Tens of thousands of spectators also noticed the NYPD counterterrorism units that were in place on the marathon course. The NYPD said it increased the number of officers on marathon duty by 10 percent this year.

“Just how many police men and women there are around — which is reassuring to see — and the barriers and all of that,” said Olivia Kennaway of Brooklyn.

The Counterterrorism Task Force also checked spectators before they entered Central Park, where the marathon ends.

“They checked my bag. They had me stand, did the wand, and sent me on my way,” said Melissa McMurphy of Joshua Tree, California.

At the finish line, the increase in security was obvious Mayor Bill de Blasio said there will be a heightened level of security throughout the city until Election Day Tuesday.

McMurphy said she “absolutely” expected the tightened security.

“It’s an election year,” she said. “We have a lot to be looking out for.”

“I feel pretty safe,” added Brian Chin of Queens.

“Coming up here for the weekend with my kids, it certainly did concern me,” added Scheungrab. “It was good to see the police out here.”

Spectators and runners said the increase in security did not get in the way of the marathon, which finished with no reported problems.