Christmas decorations outside a Madison Avenue high-rise erupted in flames Friday morning, prompting an evacuation and sending plumes of gray smoke into the sky, officials and witnesses said.

The blaze broke out at around 10:30 a.m. outside the second floor of 330 Madison Ave. in Manhattan, where holiday garland was hung, according to FDNY officials and witnesses.

There were no injuries reported.

“At first I noticed a little light on the top [of the garland]. So I said ‘What is that?’ Then I noticed smoke coming out,” said Terry Green, 57, a security guard at a building across the street.

“I said ‘Damn that might be a defective bulb.’ Then I heard ‘Buup!’ Next thing I know, I saw a fire spreading. I said, ‘Oh, sh-t, the Christmas lights are on fire1’ ” Green said.

“Standing from here, I could feel the heat. It was a lot of smoke. …It could have been a lot of worse because it started spreading to this one [other set of garland]. The Fire Department came just in time.”

The 38-story building, the global headquarters of asset management firm Guggenheim Partners, was evacuated as a precaution, according to the FDNY.

Witness Vincent Cavaliere, 50, a construction worker, called the blaze “scary.”

“I saw people in the window next to the fire peeking out. I’m yelling ‘Get out!’ ” Cavaliere said. “A couple of guys from this site ran over there with fire extinguishers. They started spraying, but it couldn’t reach.

“People were getting nervous on the street,” the man said. “They were like ‘Oh my God.’ Then the cops came and calmed everyone down. And a couple of fire trucks came and put out the fire.”