A South Africa-based disaster relief organisation on Sunday joined rescue operations in flood-hit Pakistan after Prime Minister Shehbaz Sharif appealed for international assistance to deal with the crisis.

Floods triggered by the torrential rain since June 14 have wreaked havoc, inundating a vast swathe of flat land in the south and southwest of Pakistan.

Internationally-renowned Gift of the Givers (GOTG) arrived in Pakistan on Sunday to evacuate millions displaced due to the devastating floods.

GOTG, as a rule, never intervenes in any international disaster situation unless a request for international assistance is made by the Head of State of the affected country. The Pakistani Prime Minister, Shehbaz Sharif, has now made that call just over 24 hours ago, GOTG founder Imtiaz Sooliman said on Sunday.

The organisation was at the forefront of the rescue efforts during the flash floods in 2010 and the 2005 earthquake in Pakistan.

We have immediately opened dialogue with the Surgeon General's office in the Pakistani military and Alkhidmat, a civil society organisation. Both are entities with whom we had excellent partnerships during our interventions in Pakistan with the earthquake in 2005 and the floods in 2010, Sooliman said.

The military has the resources, helicopters, boats, personnel, capability and logistics to access "cut off" areas as 60 per cent of the country is under water currently, he said.

Sooliman said the situation was an absolute tragedy , with a million homes destroyed, 33 million civilians displaced, and roads, bridges, infrastructure and sewerage systems decimated.

He expressed concern about waterborne diseases, fertile agricultural land being washed away and animals dying of hunger.

Sooliman said that although the official death toll has been given as over 1,000, the actual figure could be four to five times higher, given the volume and power of the water flooding the areas.

He said the priority requirements are tents to set up tent cities, dry food rations that can be consumed without cooking and the provision of hot meals.

The death toll from the devastating floods has crossed the 1,000-mark after another 119 people died due to deluge-related incidents across Pakistan in the last 24 hours, according to the official data on Sunday.