Australia on Wednesday advised its citizens not to travel overseas indefinitely in an attempt to slow the spread of the novel coronavirus.

The government also announced an immediate ban on non-essential indoor social gatherings of more than 100 people. That follows a ban imposed Monday on outdoor gatherings of more than 500 people.

[Getty/Kyodo]

"Don't go overseas," Prime Minister Scott Morrison said at a press conference in Canberra, as the government upgraded its travel advisory for the entire world to its highest level for the first time.

"The biggest risk we have had, and the biggest incidents of cases we have had...has been from Australians returning from overseas," Morrison said.

Australia has confirmed 452 cases of coronavirus infection, with numbers increasing rapidly each day. The country has recorded five deaths.

On Sunday, Morrison announced a 14-day self-isolation for all international arrivals in Australia, including citizens and permanent residents. Individuals found breaking their isolation requirements can be fined up to AU$50,000 ($30,000), or face jail time.

On Wednesday, the prime minister also unveiled further economic stimulus measures, including waiving various fees levied on the Australian aviation industry.

Morrison's announcement came after the country's two major airlines -- Qantas Airways Ltd. and Virgin Australia Holdings Ltd. -- announced drastic cuts to their international and domestic routes.

Qantas, the national flag carrier, said Tuesday it would cut its international capacity by 90 percent and domestic capacity by 60 percent. Virgin Australia said Wednesday it will ground all international flights and 50 percent of domestic flights from the end of March.