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

Flash floods triggered by cloudbursts in the mountainous northwest have brought destruction since Friday in the worst spell of this year's monsoon.

Pakistan has received higher-than-normal monsoon rainfall this year, triggering floods and mudslides that have killed more than 540 people since June 26.