At least 23 people have been killed after flash floods swept through eastern Afghanistan, with rescuers racing Tuesday to reach residents trapped under mud and debris.

Around 100 people are unaccounted for, the national disaster agency and the provincial governor's office said, also updating the death toll from Monday's deluge.

Agence France-Presse (AFP) reported that dozens of people gathered in remote Parun, the capital of Nuristan province, using wooden poles and their bare hands to search for the missing.

Farid Gul Zaheer, a 34-year-old pharmacist, said he had "never witnessed such a dangerous flood."

"It felt like there was an earthquake, and I heard children and people screaming," he told AFP, after getting injured while trying to flee up the mountain.