After spanning the Hudson River for more than six decades, a big chunk of the old Tappan Zee Bridge was toppled in a controlled blast Tuesday to the delight of hundreds of onlookers.

The east anchor of the venerable bridge dropped into the frigid river shortly before 11 a.m. with a flash of fire as chains kept the wreckage above the surface of the water. Its remnants will be salvaged and recycled.

A couple hundred people braved the cold to witness the bridge’s last hurrah and held out their cellphones to record the big moment.

“Blow it up! Blow it up!” they chanted before the blast sent the bridge into its watery grave — three days after Tappan Zee Constructors was forced to call off the demolition due to high winds.

“It was absolutely worth the cold. This is once in a lifetime. The concussive blast was amazing,” Mike Surdej of Brewster in Putnam County told The Post.

Pierre Belarge, of Tarrytown, said he has been photographing the bridge for a decade and had to be there.

“It was more than worth it. It was extraordinary!” he exclaimed.

Kathleen Staab, 45, of Sussex, NJ, watched from about a half-mile away with her sons, ages 4, 7 and 10.

“They’re playing hooky,” she said. “I’d rather them experience history than read about it. The fact that you can feel the concussion against your legs was crazy.”

She added: “It was always a neat bridge to drive over, and the views were always so beautiful. But it is always kind of sad to see a piece of history implode.”

For Chris Yasinsacc, the old bridge’s demise was sentimental. He said he drove up from Philadelphia for the event because his grandmother painted the bridge back in 1955.

She also was among the first to cross it, he added.

Meanwhile, Dympna Kenny, who lives next to the Scenic Hudson RiverWalk in Tarrytown, held an impromptu viewing party.

“There are about 50 people here. Some invited themselves,” said Kenny, who bought her house several years ago knowing the construction of the new bridge was coming but realizing the new one would be spectacular.

“The lights at night are gorgeous,” she said, adding that she has spent a lot of time cleaning construction dust from her windowsills.

The old span has already been replaced by the Gov. Mario M. Cuomo Bridge, which carries Interstate 87 traffic between Westchester and Rockland counties, about 30 miles north of the city.

Gov. Andrew Cuomo, the son of the new bridge’s eponym, watched the demolition by video at the Capitol in Albany.

“Boy, it went straight down,” he said as his cabinet members applauded.

But it wasn’t initially slated to go down this way.

The original plan called for cranes to pick the bridge apart piece by piece with the remains carted off by barge, according to the Journal News.

It had the support of the environmental group Riverkeeper, which feared a blast would harm the endangered Atlantic sturgeon and other marine life.

But on Sept. 8, workers said they heard a “loud pop” come off the remaining steel structure and engineers determined the bridge was unstable and feared for the safety of workers.

Tappan Zee Constructors — the company hired to build the new bridge and take down the old one — concluded that the only viable option was to blow it up.

The consortium petitioned the Federal Highway Administration, which in late December signed off on the plan to detonate explosives to take down the span’s vertical support columns.

Controlled Demolition of Maryland, the company that took down the Kosciuszko Bridge, which connected Brooklyn and Queens, in 2017, was hired for the job.

Riverkeeper’s John Lipscomb said he was assured the explosion would have limited impact on the Hudson.

“From what we’ve learned from the contractor, there isn’t an alternative that is as protective of human life,” Lipscomb told the Journal News.

“We see that they’ve gone to considerable lengths to try to figure out a way to minimize impacts to the river,” he said, adding that the timing of the blast, in the middle of winter, would limit its impact on fish.

There are plans to dismantle the western portion without explosives later this year.

With Post wires