Officials warned cyclone and monsoon season could destroy makeshift homes and cause deadly diseases to spread more rapidly in camps in Cox’s Bazar near the Myanmar border.
International Development Secretary Penny Mordaunt says the crisis is “growing daily”.
“The UK is leading the way to help vaccinate people against a deadly cholera outbreak, strengthen shelters and provide vital food and water to vulnerable Rohingya families who have already been forced to flee their homes because of brutal violence and persecution,” she said.
Hundreds of thousands of Rohingya Muslims have fled to neighbouring Bangladesh after persecution from the Myanmar military in their native state of Rakhine which began in August.
The £70m, part of a £129m contribution the UK has made since August 2017, will try to help 200,000 people with vital materials to strengthen their shelters and 300,000 people with food and safe water.
The money also aims to give emergency nutrition for 30,000 pregnant and breastfeeding women plus 120,000 children under five.
It also aims to provide access to midwifery care for 50,000 women, including many who may give birth during the rainy season, and give access to bathing cubicles for 52,900 women and girls.
It is also hoped that 50,000 people will be helped in getting access to healthcare services.
UK aid has been used in work to prepare the Cox’s Bazar camps for the monsoon season since in January when the UN estimated that 102,000 Rohingya people were living in areas at risk of flooding and 12,000 people were at risk from landslides.
Ms Mordaunt called on the Bangladeshi government to use its expertise to ensure Rohingya families are saved from the dangerous rains.
She said: “Across the globe countries were quick to respond to the plight of the Rohingya people last year, but what is needed is a longer-term commitment to these vulnerable men, women and children who have suffered so much.”