The number of people affected by a measles outbreak in Melbourne's inner north has more than doubled, and authorities are bracing for more cases to emerge in the coming weeks.

Five new cases have been reported to Victoria's Department of Health and Human Services, which brings the tally of those affected by the outbreak to nine.

They include three women and two men all aged in their 20s and 30s, two of whom have been hospitalised, a health spokesman said.

These patients are also from Melbourne's inner north - three from Brunswick, one from Brunswick West and one from Preston.