Nearly a year after Hurricane Sandy devastated the Jersey Shore, a boardwalk that was just rebuilt was ravaged by fire on Thursday, as a blaze that began at an iconic ice cream shop quickly engulfed businesses along a stretch of beach in two towns.

Flames and black plumes of smoke shot high above the Boardwalk in Seaside Park, where the fire began after 2 p.m. Within hours, strong gusts of wind swept the fire north along the adjoining Boardwalk of Seaside Heights, where a roller coaster had sat mangled in the ocean for months and became a symbol of the storm’s damage.

Funtown Pier, nearly destroyed by the hurricane, collapsed in flames. And nearby, the fire appeared to have ruined one of the Boardwalk’s two carousels. In all, about 20 businesses over a six-block stretch were almost completely destroyed, Gov. Chris Christie of New Jersey said at a news conference. Local officials suggested that number was too low.

Standing in front of emergency vehicles in Seaside Heights, he called the blaze “unthinkable.” When he heard the news, the governor said, “I said to my staff, ‘I feel like I want to throw up.’ ”