CHELYABINSK, Russia — As a small army of people worked to replace acres of windows shattered by the enormous explosion from a meteor, many joked on Saturday about what had happened in this troubled pocket of Russia.

One of the most popular jests: Residents of the meteor were terrified to see Chelyabinsk approaching.

The fireball that streaked into the sky over this tough industrial city at about sunrise Friday was undeniably traumatic. Nearly 1,200 people were reported injured by the shock wave from the explosion, estimated to be as strong as 20 Hiroshima atomic bombs.

But it also brought a sense of cooperation in a troubled region. Large numbers of volunteers came forward to help fix the damage caused by the explosion and many residents came together on the Internet — first to find out what happened and soon to make jokes.

Chelyabinsk, nicknamed Tankograd because it produced the famed Soviet T-34 tanks, can be as grim as its backbone heavy industries. Long winters where temperatures routinely hit -22 Fahrenheit add to a general dour mien, as do worries about dangerous facilities in the surrounding region.

In 1957, a waste tank at the Mayak nuclear weapons plant in the Chelyabinsk region exploded, contaminating 9,200 square miles and prompting authorities to evacuate 10,000 nearby residents. It is now Russia’s main nuclear waste disposal facility. A vast plant for disposing of chemical weapons lies 50 miles east of the city.

“The city is a place where people always seem bitter with each other,” said music teacher Ilya Shibanov. But the meteor “was one of the rare times when people started to live together through one event.”

“For most people, it’s a good excuse for a joke,” he said.

But for many, it’s provided a reason to roll up their sleeves and get to work repairing the more than 4,000 buildings in the city and region where windows were shattered, or to provide other services.

More than 24,000 people, including volunteers, have mobilized in the region to cover windows, gather warm clothes and food, and make other relief efforts, the regional governor’s office said. Crews from glass companies in adjacent regions were being flown in.

Gov. Mikhail Yurevich on Saturday said that damage from the high-altitude explosion is estimated at $33 million. He promised to have all the broken windows replaced within a week.

But that is a long wait in a frigid region. The midday temperature in Chelyabinsk was 10 degrees, and for many the immediate task was to put up plastic sheeting and boards on shattered residential windows.

Meanwhile, the search continued for major fragments of the meteor.

In the town of Chebarkul, 50 miles west of Chelyabinsk city, divers explored the bottom of an ice-crusted lake looking for meteor fragments believed to have fallen there, leaving a 20-foot-wide hole. Emergency Ministry spokeswoman Irina Rossius told Russian news agencies the search hadn’t found anything.

Police kept a small crowd of curious onlookers from venturing out onto the icy lake, where a tent was set up for the divers.

As Chelyabinsk began its healing process, residents of San Francisco, on the other side of the planet, worried that they might be next. A science institute in Northern California said it received numerous reports of a bright streak of light over the San Francisco Bay area on Friday night.

Cuba apparently experienced a phenomenon similar to the meteorite that detonated over Russia this week, island media reported, with startled residents describing a bright light in the sky and a loud explosion that shook windows and walls.

There were no reports of any injuries or damage such as those caused by the Russia meteorite.

In a video from a state TV newscast posted on the website CubaSi late Friday, unidentified residents of the central city of Rodas, near Cienfuegos, said the explosion was impressive.

“On Tuesday we left home to fish around five in the afternoon, and around 8 p.m. we saw a light in the heavens and then a big ball of fire, bigger than the sun,” one local man said in the video.