Heavy flooding has killed at least 800 people and affected one million others in Pakistan.

Officials in Pakistan say the death toll from the flooding in the past week has risen to 800, while 150 others are still listed as missing.

Flash flooding and land slides have destroyed thousands of houses in north-western Pakistan.

The city of Peshawar has been cut off and roads have been washed away.

The United Nations estimates up to one million people have been affected by the floods.

Thirty thousand troops and dozens of helicopters have been deployed, but many districts are yet to receive any help.

Footage shot from helicopters has shown people clinging to walls and rooftops as water gushes through inundated villages.

Rescue teams are struggling to reach many areas where transport and communication have been cut off.

Further rain is expected in south-eastern Pakistan in the next few days.

Flooding has already been reported in the provinces of Sindh and Punjab.

UN Office for Humanitarian Affairs spokesman Manuel Bessler says they are struggling to access some of the worst affected areas.

"The needs are first of all still search and rescue. Secondly, shelter, to have emergency [shelter] for these affected people, then food," he said.

"There is a major need for health services and then of course drinking water. We have to bring drinking water to these affected people."

Thousands of people have also lost their homes across the border in Afghanistan.