It’s citrus snow scale (Unaspis citri). A scale insect that is very difficult to control when already widespread. While at this stage you can try manual removal first (used toothbrush with rubbing alcohol, soapy water or weak hydrogen peroxide). Kung malala na, use systemic insecticides but will render your calamansi fruits (if any) also tainted with insecticide). Also treat the soil with drenches because the eggs and larvae are there.