With physical distancing in full swing and authorities applauding Australians for mostly staying at home, returning travellers loom as a major coronavirus threat.

Key points: Chief Medical Officer Brendan Murphy said Australia was "in a good place" but could not afford to get complacent

Chief Medical Officer Brendan Murphy said Australia was "in a good place" but could not afford to get complacent Professor Murphy said most new cases in the next week would likely be from travellers returning home

Professor Murphy said most new cases in the next week would likely be from travellers returning home More than 100 Australians from the coronavirus-stricken Greg Mortimer cruise ship touched down in Melbourne on Sunday morning

Chief Medical Officer Brendan Murphy said Australia was "in a good place" but could not afford to relax social-distancing measures now, with community transmission capable of spreading the virus rapidly.

"We have had a continual reduction in the number of new cases each day," he said.

"There is no place in the world I would rather be than Australia at the moment.

"Having said that, as my colleagues have been saying for the past few days, we cannot become complacent. We still have some community transmission … which [does] mean that there are people in the community that are transmitting this virus."

Professor Murphy said the "biggest risk" to Australia in coming days and weeks was returning travellers.

Australians are currently banned from travelling overseas and the borders are closed to non-residents, but they are open for those Australians overseas who can find their way home.

On arrival in Australia, they have to spend a mandatory two weeks in quarantine.

"Two thirds of our cases in Australia are returned travellers or tourists, mostly around citizens coming back," he said.

"In fact, it is likely the new cases we will see over the next week will be returned travellers."

More than 100 people from the coronavirus-stricken Greg Mortimer cruise ship have touched down in Melbourne today, going straight into 14 days of quarantine, while flights have been chartered all around the world to scoop up travellers and bring them home.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 58 seconds 58 s The Greg Mortimer cruise ship docked in Uruguay before passengers caught a chartered flight to Melbourne.

Professor Murphy said strict border controls would have to remain in place until the virus was no longer a major problem around the world.

And as long as that is the case, or until a vaccine is developed and distributed, some form of stay-at-home orders will likely be imposed on Australians.

Stay up-to-date on the coronavirus outbreak Download the ABC News app and subscribe to our range of news alerts for the latest on how the pandemic is impacting the world

"We have always said that measures of some sort will need to be in place for several months," he said.

"What form that will take, and how stringent they are, depends upon the epidemiology at the time, but we have always said you could not put huge measures in for four to six weeks and suddenly remove them and life would go on. That is an unrealistic position.

"Australians are learning to behave differently. You have all seen it when you walk into shops. You have seen people obeying the rules, people washing their hands. More in the last month than some have done in a year.

"These are great changes in our psyches."