When war came, it was time to go. Stories on the Kupiansk bridge.

Crossing the slender span of ragged concrete above the Oskil River – all that remains of what was once the Kupiansk bridge – was an exhausted and emotional migration of people, both civilian and military, navigating a war zone.

With Ukraine pressing an advance that had already forced a Russian retreat from more than 3,000 square miles of occupied territory in eastern Kharkiv province, the bombed bridge was the only path for Ukrainian civilians east of the Oskil to escape the increasingly destructive battlefront.

As Ukraine rushed armored columns east across two floating pontoon bridges late last week, the air shook with the steady concussion of outgoing Ukrainian artillery. A Russian drone whirred overhead, looking to target the critical crossing points and sending soldiers hurrying for cover.

Caught between Ukraine’s advances and Russian defenses are villages and towns east of the Oskil that for seven months of Russian occupation were spared the war’s most destructive forces but have now been transformed into its front.

The result is a sudden exodus of civilians seeking safety, who thread their way over what is left of the bridge. Along with their few bags and some pets, they carry stories of survival, resilience, and raw emotion as the war has swept over them.

In a final, grotesque reminder of the conflict they are leaving behind, evacuees must walk past the body of a Russian soldier lying as a silent sentry at the eastern end of the bridge.

“When the Russians ran away, they shot at everyone, and destroyed everything,” says one man, from a cluster of evacuees awaiting transport. They sometimes flinch when a Ukrainian artillery team – unseen, but nearby – launches shells toward Russian positions.

In the first day of organized evacuations Thursday, 750 people crossed, according to volunteers who shuttle them westward to Kharkiv. On Friday by 1 p.m., already 500 to 600 had crossed.

Ukrainian forces over the weekend captured the strategic rail hub of Lyman, 50 miles southeast of Kupiansk, after encircling the town and triggering a chaotic Russian withdrawal. Moscow later said Russian forces had been ordered back “to more advantageous lines.”

Control of Lyman by Ukraine will not only hamper Russian reinforcement and resupply efforts in the eastern Donbas region – which President Vladimir Putin has described as the focus of the Russian invasion after failing to seize the Ukrainian capital of Kyiv last March – but also provide a launchpad for deeper Ukrainian advances into Russian-controlled territory.

Mr. Putin on Friday announced that Russia had annexed two regions that make up the Donbas, along with the Kherson and Zaporizhzhia regions to the south, and that all Ukrainian residents there would henceforth be Russian citizens “forever,” after hastily arranged and widely condemned referendums last week.

Any attack on them would be considered an attack on the Russian homeland, he said. But Mr. Putin did not mention recent battlefield setbacks, nor the fact that Moscow does not control all of any of the so-called incorporated regions.

“The war is here. Go.”

Such high-level political maneuvering means little to those caught in the counteroffensive.

“We don’t want to leave our home,” says Gulfira Kharasik, a pensioner in a pale maroon jacket, wiping away a tear. She stands amid a group that had just crossed over the bridge and the marshy expanse of the Oskil River basin Friday and was awaiting transfer to the west.

“There was shelling for a week, but yesterday and last night it was very tough,” she says. “The whole area was bombed.”

In the end, a chain of events that brought the war home made her family’s decision to flee inevitable. First, a Russian tank set up position next to the fence of their summer house in the village of Hlushkivka, 9 miles southeast of Kupiansk – making the home her parents had built decades earlier an obvious Ukrainian target.

Ms. Kharasik’s husband, Ivan, also a retiree and wearing a sweat-stained “England” cap, says he then set off from the summer house on foot the 3 miles north to the family apartment at Kivsharivka. Along the way, a bomb dropped by a Russian plane landed very close to him.

“I was thrown a meter,” he says of the blast.

Mr. Kharasik sought shelter in a basement, but was found by Russian troops. He says they told him, “The war is here. Go.”

Upon reaching the apartment where his wife and adult son, Dmytro, were staying, the shelling intensified. The family describes a direct hit on a nearby apartment block that killed two of their neighbors, whom they saw were thrown outside by the blast.

They know another neighbor who died, also.

Dmytro shows a picture on his phone of where the local Orthodox church once stood, across the street from his house. Aged and made of wood, it was hit and burned to the ground.

“Now it is only a fence,” he says of all that is visible in the photograph.

Evacuating wounded people

Russian lines have been falling back from Kupiansk. Witnesses who visited the city days earlier describe being able to hear Ukrainian shells landing much closer, on the east side of the Oskil. On Friday, the targets of the steady Ukrainian shelling were farther away, and the impacts could rarely be heard.

Ukrainian soldiers say the east side of the river is still not “cleaned” entirely of Russians, with many of them still hiding. But their bigger concern Friday was an expected artillery barrage on the pontoon bridges across the Oskil that saw constant military traffic feeding the advancing counteroffensive.

At a muddy intersection on the west side of the river, in a residential area that blocked any view of the pontoon crossings, a handful of Ukrainian soldiers jumped up at the sound of a Russian surveillance drone overhead and hid beneath a metal awning.

They say one soldier was killed and three wounded in attacks on the bridges in the previous two days. Anywhere near the river, military vehicles were parked under trees or bushes to avoid easy detection from the air.

The remains of the concrete bridge also serve as an exit from the battlefield for wounded Ukrainian soldiers. In one case, four soldiers used a makeshift canvas stretcher to carry a wounded comrade to a waiting ambulance.

In another, a soldier with his head bandaged began the walk alone, only to be joined by another, who wrapped his arm around the wounded man to support him.

The soldiers are skittish, but so are the evacuating civilians, who say they had little choice but to flee as the war came to them.

Among one group of evacuees, there were stories about recent nights spent in basements, about witnessing rocket fire from both sides, and, in one case, about a neighbor killed by shrapnel and left lying in a backyard.

Oksana Gagarinova holds her 2-year-old son Timur close, as tears well up in the baby’s eyes.

At least now, after seven months of Russian occupation, these families are able to evacuate to Ukraine and not to Russia – the only option before, says Svitlana Gulakova. She stands at the western end of the Kupiansk bridge with her teenage son and a cluster of others who just walked across the sliver of concrete.

They are anxious and emotional, but also relieved, as they await a volunteer van to take them to the next, safer place.

“There is shelling there now, so it is impossible to live,” says the bespectacled Ms. Gulakova of her home village. “It made us leave everything.”

Igor Ishchuk supported reporting for this story.