The United States is the country of origin for most of the coronavirus cases in Australia, the prime minister has said.

Speaking on 2GB this morning, Scott Morrison said now was the right time to close the nation's borders.

"We were able to slow the virus' start and spread in Australia through these early periods," Mr Morrison said.

Pictures: Coronavirus (COVID-19) outbreak around the world

"The country which has actually been responsible for a large amount of these (coronavirus cases) has actually been the United States.

"At the end of the day, that's a function of the number of people who travel between the US and Australia."

Eighty percent of coronavirus cases in Australia are people who have come in from overseas or have caught the disease directly from them.

A failure to conduct adequate numbers of coronavirus tests meant the United States appeared to have many more infections in recent weeks than had been announced.

Mr Morrison dismissed a suggestion from host Alan Jones that China should be excluded from bidding on devalued assets because the coronavirus stemmed from that country.

"I don't think there's any suggestion that any country, including China, has done anything deliberately," he said.

"This is a virus. It originated in Wuhan, China, and has gone around the world."

Mr Morrison defended a $715 million support package for the aviation industry not going directly to employees.

"That money is going to keep the aviation industry alive," he said.

"Companies are going to go through incredibly difficult times over the next six months, we're going to help them as much as we can and help them keep jobs wherever we can."

Mr Morrison noted the $715 million package was not a cash handout but a waiver on fees.

Yesterday 20,000 Qantas employees were sent home and asked to use their leave entitlements as the coronavirus pandemic took a heavy toll on the industry.



