In 1941, Wong took a St John Ambulance nursing course and joined the nursing team at a medical centre in Havelock Road. When the sister-in-charge was transferred elsewhere, Wong took over the running of the centre. In February 1942, days before the Japanese invaded Singapore, May and her children left for Australia. She returned after the war, and resumed her charity work. In 1948 she organised the Keppel Harbour Feeding Centre to provide food for hungry children.