Shopkeeper Nazer Mohammad ran home as soon as he heard about flash floods crashing through the outskirts of Pul-e-Khumri, a provincial capital in northern Afghanistan. By the time he got there, all had been swept away, including his home and family of five.

“Everything happened just all of a sudden. I came home, but there was no home there. Instead, I saw all the neighbourhood covered by mud and water,” said Mohammad, 48. He buried his wife and sons, aged 15 and eight years, but he is still looking for two daughters, aged about six and 11 years.

The United Nations World Food Programme (WFP) estimates that unusually heavy seasonal rains in Afghanistan have caused more than 300 deaths and destroyed thousands of houses, most of them in the northern province of Baghlan, which bore the brunt of the deluges on Friday.

Mohammad said he found the bodies of his wife and two sons late on Friday night on the outskirts of Pul-e-Khumri.

“I hope someone has found my daughters alive,” he said, holding back tears. “Just in the blink of an eye, I lost everything: family, home, belongings. Now nothing is left to me.”

More than 50 children have been killed, according to UNICEF, one of several international aid groups sending relief teams, medicines, blankets and other supplies. The World Health Organization delivered 7 tonnes of medicines and emergency kits.

Save the Children said about 600,000 people, half of them children, live in the five districts in Baghlan that have been severely affected by the floods. The group said it sent a “clinic on wheels” with mobile health and child protection teams to support children and their families.

“Lives and livelihoods have been washed away,” said Arshad Malik, country director for Save the Children. “The flash floods tore through villages, sweeping away homes and killing livestock. Children have lost everything. Families who are still reeling from the economic impacts of three years of drought urgently need assistance.”

He said Afghanistan is a country least prepared to cope with climate change patterns, such as the heavier seasonal rains, and needs help from the international community.

At least 70 people died in April from heavy rains and flash floods, which also destroyed about 2,000 homes.