Australian officials are closing the border between Australia’s two most populous states — Victoria and New South Wales — for an indefinite period as they scramble to contain an outbreak of the coronavirus in the city of Melbourne.

Officials last blocked movement between the two states in 1919 during the Spanish flu pandemic.

The number of Covid-19 cases in Melbourne, Victoria’s capital, has surged in recent days, prompting authorities to enforce strict social-distancing orders in 30 suburbs and put nine public housing towers into complete lockdown.