The clock sits frozen, forever recording a moment in time: 8:50 a.m., Sept. 11, 2001.

Artist Edwin Class received the battered timepiece from a worker at ground zero shortly after the terrorist attack on the World Trade Center. The first plane hit the tower at 8:46 a.m.; the clock somehow survived where so many people did not.

The find is now part of a multimedia New-York Historical Society exhibit chronicling the emotions that washed across the city after Sept. 11. “Missing: Streetscape of a City in Mourning” opens today to the public.

The stopped clock, collected by Class while he worked as a volunteer after the attacks, is among the more disturbing exhibits.

“I’m an artist, and this is just how I responded to what I saw,” explained Class, who collected dozens of items at the site. “I was just doing this to get it out of my system.”

Class’ collection fits perfectly in the exhibit’s random style: photographs, video, pieces of impromptu memorials that cropped up around the city  about 150 items.

Included is a Halloween costume from last year’s Greenwich Village parade, showing papier-mache twin towers adorned with wings and a halo.

There are 15-foot rolls of butcher paper collected from Union Square Park, each filled with hand-scrawled messages of conflicting emotions.

And there is a wooden firefighter carved by Dave Fontana of Brooklyn’s Squad One, who was one of 10 firefighters from the Park Slope firehouse killed when the towers collapsed. The statue stood for months outside the firehouse in tribute to the lost firefighters.

The wooden firefighter, while hardly a typical museum piece, turned out to be perfect for this exhibit.

“Two days after it happened, our president, Ken Jackson, brought the whole staff together and said we had to do something,” said Travis Stewart, a society spokesman. “We just didn’t know what.”

They soon found out, creating a collection that mingles candles from street memorials, toy fire trucks, a teddy bear in firefighter’s garb, a John Lennon figurine.

The wide-ranging artifacts display the scope of how people mourned and what artists produced after living through such a tragedy, Stewart said. The collection was assembled in conjunction with City Lore, a group of folklorists and artists.

Some of the items are more uplifting and hopeful, like a photograph of a dust-covered fire truck with the words “BLESS YOU” rubbed in the ashes. There are also hundreds of messages left near ground zero, honoring the dead.

Class used some of the items he found in lower Manhattan as an inspiration to make new art. He created a series of construction helmets painted with World Trade Center themes, and an American flag made from tiny bags of the ash that covered all of lower Manhattan for weeks after the attacks.

The exhibit is designed to be a companion piece to an existing one at the Historical Society titled “WTC: Monument.” Conceived before the collapse of the towers, that exhibit details the remarkable efforts made to construct the World Trade Center.