Cyclone Dineo, which reached landfall late on Wednesday, is thought to be Mozambique's worst storm in ten years. It's destroyed homes, disrupted electricity supplies and caused flooding across southern areas of Mozambique.
The cyclone struck shortly before the maize harvest season, with Mozambique already struggling to recover from its worst drought in more than three decades.
Joseph Kamara, Humanitarian and Emergency Affairs Director for World Vision's Southern Africa Region, said: "This is going to be a major catastrophe in the area, so we're looking at 750,000 people being affected directly.
"This number could increase or reduce, depending on the assessments that... we're conducting."
World Vision is expecting to begin distributing emergency kits, which contain cooking pots, water purification tablets and mosquito nets, as soon as Saturday.
Mosquito nets are needed to help prevent a spike in malaria, a disease which could be exacerbated by the stagnant floodwaters.
For every family in Mozambique receiving urgent supplies from the charity, 99 face being turned away.
World Vision expects 200,000 thousand emergency kits will be required, with only around 2,000 available.
Joseph Kamara added: "Because of the large number of people affected and we have very few kits to distribute, it's going to be very difficult. So, we're going to try and look at [prioritising] those who are worse off than others."