Buner, Pakistan — Pakistan issued a flood alert Wednesday for some southern districts, warning of torrential rains, as rescue teams continued searching for missing people in the country's northwest, where severe floods killed hundreds over the past week.

Officials stress that a cloudburst is a rare and scientifically defined phenomenon, triggered by orographic effects in the atmosphere—when moisture-laden air is rapidly lifted over mountainous terrain, causing sudden, extremely heavy rainfall over a small, localised area.

More than 20 people have died on Wednesday in a torrential spell of monsoon rain in Pakistan, where downpours have swept away entire villages over the last week, killing more

A deluge of rain triggered floods and landslides, sweeping people away and flooding and destroying homes, officials said.

Pakistan has restored 70% of electricity and reopened damaged roads in the north and northwest after flash floods killed more than 300 people.

Khyber Pakhtunkhwa government's MI-17 helicopter had taken off from Peshawar for Bajaur when contact was lost over Mohmand tribal district, according to initial reports.