Across Mozambique it is estimated that 1.8 million people have been affected by the cyclone, which also ravaged parts of Malawi and Zimbabwe.
Aid due to be delivered by an RAF aircraft is expected to include solar lanterns, water purifiers and shelter kits, the Ministry of Defence said.
The A400M Atlas aircraft will help provide relief for the 37,500 people in need of urgent shelter when it departs for Mozambique early this week, amid reports that at least 17,400 homes have been destroyed by the cyclone and subsequent flooding.
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Unicef's executive director Henrietta Fore has said it is a "race against time to help and protect children".
She tweeted: "We're assisting those sheltering in schools, setting up emergency medical tents, helping reunite separated families, and looking after orphaned children. Things will get worse before it gets better."
Defence Secretary Gavin Williamson said: "Our partners across the globe can count on our Armed Forces to lend a helping hand in times of need, which is why are sending an RAF aircraft to assist with the aid relief."
The UK is also sending forklift trucks and other equipment to help quickly unload aid from planes and cut the time it takes to get relief items to those in need, International Development Secretary Penny Mordaunt announced on Friday.
The UK's total support for the survivors of Cyclone Idai now stands at £22 million, including £4 million of aid-match money for the Disaster Emergency Committee's appeal.
Eight million pounds was raised in the first 24 hours of the DEC's appeal, including personal donations from the Queen and Prince of Wales.