A moldy old grenade with the pin still in place was found at a construction site in lower Manhattan on Monday afternoon, prompting police to evacuate the block and summon the bomb squad.

The device, which was declared inert, was found at 221 Bowery around 1 p.m. by construction workers, cops and witnesses said.

Construction foreman Yzaul Abreu, 27, said the grenade was ”full of mold” and “wrapped up in a napkin” in a bucket when he found it.

“It had the pin in it,” Abreau said through an interpreter.

Abreau was fearful because of gas lines in the basement and carried the grenade to the first floor, where the bomb squad retrieved it.

“He was terrified, scared almost tearing,” said Estarlin Torres, 19, a construction assistant.

Abreau said the grenade fit in the palm of his hand.

“I don’t know if it was active,” Torres said. “All I know is that the pin was in it.”

The whole block was evacuated for between 30 and 40 minutes.

“We were just waiting outside. They put the yellow tape. The stores closed, too,” Torres said.

The stores that closed included Bowery Iconic Magazine at 215 Bowery and Chair Up at 219 Bowery.