A murmuring madman with a giant machete straight out of the Amazon slashed a tourist during a broad-daylight attack in Bryant Park on Tuesday — terrifying the bustling lunchtime crowd.

Sook Yeong Im, who is visiting from South Korea, had just finished a yoga class on the lawn and was looking for a place to sit around 11:30 a.m. when career criminal Frederick Young, 43, followed her with the blade in a plastic bag.

“She felt suspicious and was trying to avoid him and started walking faster,” said Saya Dajung, 35, a Brooklyn art instructor who was teaching a class in the park.

Young — who has at least two dozen prior arrests, including a 2010 machete attack — hacked at the victim’s arm several times as she screamed.

“He was trying to hurt her more but because she was yelling, other people came, and he couldn’t,” said Dajung.

Parkgoers rushed to her aid, including one person who used a belt as a tourniquet.

“She is so freaked out because she was bleeding a lot,” Dajung said. “I could see the muscles in her arm.”

NYPD Chief of Detectives Robert Boyce said that Im suffered a “substantial gash on her right arm.”

She was rushed to Bellevue Hospital in stable condition.

Young, who also had a screwdriver on him, was chased by park security and several witnesses to the park’s south side.

Cops were flagged down, and he was arrested without a fight.

Young was charged with assault, cops said.

“I point my weapon at him and order him to drop his weapon,” said Detective Jason Norman, one of the arresting officers. “The suspect complies and drops his weapon out of his left hand.”

Preston Victor, 51, one of the park security guards, said Young had the machete in a plastic bag when he first attacked Im.

“It looked like a towel” until the blade poked through the bag, he said. “But then the sharpness of the blade came out of the bag, and you could see him hitting her with the blade.”

Im was originally planning to return to South Korea Sunday.

“She can’t move her fingers now, but the doctors say she will be OK,” Dajung said. “They are really freaked out. This doesn’t happen in South Korea.”

Additional reporting by Larry Celona and Antonio Antenucci