Theresa May is to announce plans to boost Britain's investment in Africa after Brexit, during her first trip to the continent as prime minister.
At a speech later, May will say she is "unashamed" about ensuring Britain also benefits from its aid spending.
And speaking on her way to Cape Town, she played down warnings from the chancellor about the economic damage a no-deal Brexit could cause.
She will also visit Nigeria and Kenya during the three-day trade mission.
The trip - which will see May meet the presidents of all three countries - aims to deepen economic and trade ties with growing African economies ahead of Britain leaving the EU in 2019.
Talking to journalists on board RAF Voyager on Tuesday morning, May reiterated that she believed a no-deal Brexit was still better than a bad deal - adding no-deal "wouldn't be the end of the world".
Arriving in South Africa on Tuesday morning, May is expected to say she wants the UK to overtake the US to become the G7's biggest investor in Africa by 2022.
She will announce an "ambitious new approach" to the UK's aid spending in Africa, by using it to help British private sector companies invest on the continent, reports BBC.
Private sector investment is key to driving growth and "unleashing the entrepreneurial spirit" in Africa, she will say.
In her speech, Mrs May is expected to say that creating jobs on the continent - where many countries have young populations - is "in the world's interest".
It is the best way to tackle extremism, instability and migration to Europe, Mrs May will claim, adding that otherwise the environmental and economic impacts will reach every corner of the world.
The prime minister, who is being accompanied by business leaders and ministers during her visit, will also set out her aim for the UK to be the "number one investor in Africa" out of the G7 group of developed nations by 2022.
The UK's overseas aid budget totalled £13.9 billion in 2017, an increase of £555 million in 2016.
UK direct investment in Africa was £42.7 billion in 2016, compared to £44.3 billion from the US, £38 billion from France and £31 billion from China, according to data from the United Nations Conference on Trade and Development.
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