Heavy seasonal rains have set off flash floods across Afghanistan, killing more than 300 people in one province and destroying thousands of homes, according to United Nations officials. The floods have displaced thousands of others and engulfed entire villages, Afghan officials say.

The flood’s toll in the northern province of Baghlan, which appeared to have suffered the worst devastation, was likely to rise, said Hedayatullah Hamdard, the director of the provincial disaster management department. Most of the dead there were women and children, he said. At least 2,000 homes have been destroyed, according to the U.N. World Food Program.

Flooding began around 4 p.m. Friday and continued into the evening in Baghlan Province. Abdul Aziz Ayyar, a tribal elder, was in his home in the Baghlan-e-Markazi District when rain began pouring down. He stepped outside and saw a torrent of water rushing down a nearby mountain toward his village.

He grabbed his two children and wife and began sprinting to a different nearby mountain, shouting as he ran to warn the other villagers, he said. His 30-year-old niece was running behind him, carrying her 1-year-old and 3-year-old daughters. At one point, his niece tried to grab his hand to steady her and her children, he said, but before he could grab her, floodwater crashed over them, carrying them away.

“We returned to the village after midnight to save people, but they were all dead,” Mr. Ayyar said on Saturday. “Everything was flooded. There are three villages in our area where no houses are left; all have been razed by the flood.”

Flooding also killed at least one person in Badakhshan, a mountainous eastern province, where homes, small dams and bridges were destroyed and 2,000 livestock were killed, the provincial diaster management department said.

The provinces of Ghor and Herat, in central and western Afghanistan, were also affected by flooding, according to the Taliban authorities. And doctors were being deployed in Parwan Province — north of Kabul, Afghanistan’s capital — said Hekmatullah Shamim, the spokesman for the province’s governor, though details of the toll there were not immediately available.

Rescue teams were sending food, aid, medical teams and ambulances to the affected areas of Baghlan Province, said Sharafat Zaman, a spokesman for the Health Ministry.

Barkatullah Sulaimani, a school principal in the Haji Wakil village of the Burka District, said on Saturday that when floodwater began rushing through his village, he ran to a hilltop on its outskirts. By about 11 p.m. Friday, he said, about 100 people from Haji Wakil had made it to safety, but nearly every family was missing some relatives. About 200 people from the village were unaccounted for, Mr. Sulaimani said.

Throughout the night, he took calls from people who were not in the village at the time of the flood and were seeking information about missing relatives.

“I told them I don’t see anything but water,” Mr. Sulaimani said. “They are not with us here. Maybe they are dead or alive.” Of their village, only some walls of some houses.

In recent years, Afghanistan has experienced a dire economic crisis, faced a spate of natural disasters, and dealt with the turmoil of war and clashes with its neighbor Pakistan.

The wet conditions this year have been brought on in part by the El Niño phenomenon, raising the risk of floods, which hinder crop production and the flow of food supplies, particularly in the country’s north and northeast, the International Rescue Committee said in a statement last week.

Flash floods from heavy rains inundated much of Afghanistan last month, killing more than 100 people, destroying more than 1,000 homes and ruining more than 60,000 acres of farmland, the group said.

The damage to roads, bridges and the power infrastructure could hinder the delivery of humanitarian aid there, it said. Floods are also economically devastating in a country where at least 80 percent of the population derives its income from agriculture, according to the United Nations.

“Any additional flooding will have a detrimental impact on large swaths of the population,” the International Rescue Committee said, “which are already reeling from an economic collapse, high levels of malnutrition and conflict.”

John Yoon contributed reporting from Seoul.