Chief Medical Health Officer Dr. Paul Van Buynder says one child from the Fraser Valley has been admitted to hospital so far.
He says the best protection against the disease is two doses of vaccine.
Arrangements are being made to have more vaccine distributed to doctors and pharmacies from Abbotsford to Hope, and vaccination clinics are being set up.
The authority says children under five years old are the most at risk of serious disease and need to get a vaccinated.
Word of the outbreak came last weekend when the authority reported that two people had measles in Chilliwack, but it now says the disease has spread through the general population in Chilliwack and Agassiz.
Also on HuffPost