MOSCOW — Gym class came to a halt inside the Chelyabinsk Railway Institute, and students gathered around the window, gazing at the fat white contrail that arced its way across the morning sky. A missile? A comet? A few quiet moments passed. And then, with incredible force, the windows blew in.

The scenes from Chelyabinsk, rocked by an intense shock wave when a meteor hit the Earth’s atmosphere Friday morning, offer a glimpse of an apocalyptic scenario that many have walked through mentally, and Hollywood has popularized, but scientists say has never before injured so many people.

Students at the institute crammed through a staircase thickly blanketed with glass out to the street, where hundreds stood in awe, looking at the sky. The flash came in blinding white, so bright that the vivid shadows of buildings slid swiftly and sickeningly across the ground. It burst yellow, then orange. And then there was the sound of frightened, confused people.

Around 1,200 people, 200 of them children, were injured, mostly by glass that exploded into schools and workplaces, according to Russia’s Interior Ministry. Others suffered skull trauma and broken bones. No deaths were reported. A city administrator in Chelyabinsk said that more than a million square feet of glass shattered, leaving many buildings exposed to icy cold.

And as scientists tried to piece together the chain of events that led to Friday’s disaster — on the very day a small asteroid passed close to Earth — residents of Chelyabinsk were left to grapple with memories that seemed to belong in science fiction.

“I opened the window from surprise — there was such heat coming in, as if it were summer in the yard, and then I watched as the flash flew by and turned into a dot somewhere over the forest,” wrote Darya Frenn, a blogger. “And in several seconds there was an explosion of such force that the window flew in along with its frame, the monitor fell, and everything that was on the desk.”

“God forbid you should ever have to experience anything like this,” she wrote.

At 9 a.m., the sun had just risen on the Ural Mountains, which form a ridge between European Russia and the vast stretch of Siberia to the east. The area around Chelyabinsk is a constellation of defense industry manufacturing cities, including some devoted to developing and producing nuclear weapons. The factory towns are separated by great expanses of uninhabited forest.

As residents of Chelyabinsk began their day on Friday, a 10-ton meteor around 10 feet in diameter was hurtling toward the Earth at a speed of about 10 to 12 miles per second, experts from the Russian Academy of Sciences reported in a statement released Friday. Scientists believe the meteor exploded upon hitting the lower atmosphere and disintegrated at an altitude of about 20 to 30 miles above the Earth’s surface — not an especially unusual event, the statement said.

This meteor was unusual because its material was so hard — it may have been made of iron, the statement said — which allowed some small fragments, or meteorites, perhaps 5 percent of the meteor’s mass, to reach the Earth’s surface. Nothing similar has been recorded in Russian territory since 2002, the statement said.

Estimates of the meteor’s size varied considerably. Peter G. Brown, a physics professor and director of the Center for Planetary Science and Exploration at the University of Western Ontario, said it was closer to 50 feet in diameter and probably weighed around 7,000 tons. He said the energy released by the explosion was equivalent to 300 kilotons of TNT, making it the largest recorded since the 1908 Tunguska explosion in Siberia, which is believed to have been caused by an asteroid.

Meteors typically cause sonic booms when they enter the Earth’s atmosphere, and the one that occurred over Chelyabinsk was forceful enough to shatter dishes and televisions in people’s homes. Car alarms were triggered for miles around, and the roof of a zinc factory partially collapsed. Video clips, uploaded by the hundreds starting early Friday morning, showed ordinary mornings interrupted by a blinding flash and the sound of shattering glass.

Maria Polyakova, 25, head of reception at the Park-City Hotel in Chelyabinsk, said it was the light that caught her eye.

“I saw a flash in the window, turned toward it and saw a burning cloud, which was surrounded by smoke and was going downward — it reminded me of what you see after an explosion,” she said. The blast that followed was forceful enough to shatter the heavy automatic glass doors on the hotel’s first floor, as well as many windows on the floor above, she said.

Valentina Nikolayeva, a teacher in Chelyabinsk, described it as “an unreal light” that filled all the classrooms on one side of School No. 15.

“It was a light which never happens in life; it happens probably only in the end of the world,” she said in a clip posted on a news portal, LifeNews.ru. She said she saw a vapor trail, like one that appears after an airplane, only dozens of times bigger. “The light was coming from there. Then the light went out, and the trail began to change. The changes were taking place within it, like in the clouds, because of the wind. It began to shrink and then, a minute later, an explosion.”

“A shock wave,” she said. “It was not clear what it was, but we were deafened at that moment. The window glass flew.”

The strange light had drawn many to the windows, the single most dangerous place to be. Tyoma Chebalkin, a student at Southern Urals State University, said that the shock wave traveled from the western side the city, and that anyone standing close to windows — security guards at their posts, for instance — was caught in a hail of broken glass.

He spoke to Vozhd.info, an online news portal, four hours after the explosion, when cellphones, which had been knocked out, were still out of order. He said that traffic was at a standstill in the city center, and that everyone he could see was trying to place calls. He said he saw no signs of panic.

In those strange hours, Ms. Frenn, the blogger, wrote down the thoughts that had raced through her mind — radiation, a plane crash, the beginning of a war — and noted that her extremities went numb while she was waiting to hear that the members of her family were unhurt.

When emergency officials announced that what had occurred was a meteor, what occurred to her was: It could happen again.

“I am at home, whole and alive,” she wrote. “I have gathered together my documents and clothes. And a carrier for the cats. Just in case.”