South African President Cyril Ramaphosa has declared a national state of disaster and announced a range of measures to respond to the rain-triggered devastating floods in which over 400 people have died, dozens are still missing and more than 40,000 left homeless across the coastal province of KwaZulu-Natal (KZN).

The new state of disaster follows just a fortnight after Ramaphosa announced the end of one that was imposed for over two years due to the Covid-19 pandemic.

The floods followed four days of unprecedented torrential rain, which Ramaphosa said on Monday could be attributed to climate change.

The president said that although a provincial state of disaster had been declared last week in KZN, the flooding has disrupted fuel lines and food supplies to the entire country from Durban, which is South Africa's main port of entry and the largest on the African continent.

Rescuers searched for dozens of people still missing in KZN after heavy rains in recent days triggered floods and mudslides that have killed more than 400 people.

The floods have left thousands homeless, knocked out power and water services and disrupted operations at one of Africa's busiest ports, Durban.

Ramaphosa said there were also signs that imminent adverse weather conditions could also affect other provinces.

This had necessitated the national state of disaster, he said.

Numerous roads and bridges have also been destroyed, with the defence force now tasked to assist in repairing the massive damage to infrastructure.

Ramaphosa said the national state of disaster would enable the mobilisation of more resources, capabilities and technical expertise in providing relief, recovery and rehabilitation to affected areas with national, provincial and local governments working together to address the challenges.

He announced a three-phased plan to respond to the disaster.

"First, we will focus on the immediate humanitarian relief, ensuring that all affected persons are safe and that their basic needs are met. Second, we will focus on stabilisation and recovery, rehousing people who have lost homes and restoring provision of services. Thirdly, we will focus on reconstruction and rebuilding as many areas as destroyed and devastated including infrastructure, Ramaphosa said.

I have authorised the South African National Defence Force to bring in more personnel, water storage and purification supplies and engineering teams to assist with electricity as well as water restoration, he added.

The president said preparations were underway to provide temporary residential units and it is expected that construction of these temporary shelters should begin by the end of this week.

"Financial assistance through a voucher system is being made available to assist households to rebuild partially damaged houses. A national team of project managers and engineers have been deployed in the province to assess the damage and to advise on the rebuilding, he said.

Announcing the immediate deployment of a billion rand from the Treasury for this purpose, Ramaphosa said a wide range of organisations and individuals from the private sector with specialist expertise would be used to ensure that the funds are not misused or stolen, as had happened with emergency funding during the Covid -19 pandemic, which is still being uncovered.

"There can be no room for corruption, fraud or mismanagement of any sort. Learning from the experience of the Covid -19 pandemic, we are drawing together various stakeholders to be part of an oversight structure to ensure that all funds disbursed to respond to this disaster are properly accounted for and that the state receives value for money.

"We are determined that there must be transparency and accountability as the projects are costed and implemented, as well as how resources are deployed right from the beginning; not after the money has been either wasted or stolen, Ramaphosa emphasised.

The president's national broadcast came as scores of relief organisations from all over the country scrambled to get water, food and clothing to thousands of people in KZN, with many areas accessible only by helicopter.