Weddings must be limited to the couple, celebrant and two witnesses, while funerals could only be attended by about 10 people.
Exceptions will include aid workers, those who need to travel on compassionate grounds or for people whose travel is essential for work.
He added that states and territories are considering whether to introduce criminal charged against those who organise house parties - a "nightclub" at home, as PM Morrison described them.
Hairdressers and barbers can continue but must strictly manage social distancing and restrict the amount of time a patron can be in the premises to no more than 30 minutes.
"Large gathering for weddings, sadly, will not be possible".
Australia is enforcing more stringent controls to slow the spread of the coronavirus, banning non-essential travel overseas, closing food courts in shopping malls and restricting weddings and funerals after the number of cases surged past 2,000.
The Prime Minister also announced the government will be making it offence for people to buy goods in bulk in Australia in attempt to profiteer overseas.
Funerals will be restricted to no more than 10 people.
"If we do all the things that [chief medical officer] Dr Murphy has outlined, and these other quite strict measures we have put in place about areas of social gathering ...stopping all those things we believe will have a really significant impact, we would hope, on the spread of the virus".
The government is able to do this through biosecurity powers that are handed down from the Governor General.
"People defying that advice and looking to go overseas on leisure travel, they (now) can't do that because when they come home they put Australians at risk".
"Australians that have lost their jobs lost hours of work, businesses that have been forced to close their businesses, these are heartbreaking events in our nation's history and story".
"We are not unconscious of the real impact these measures are having on the lives of daily Australians so we will continue to do everything we can, both as a Federal Government and at State Government and Territory Governments around the country, to do all we can to support our people through what is going to be an incredibly hard time".
It is safe to send children to school up to the end of the term.
A group of experts from the Group of Eight universities, asked by the chief medical officer to advise on social distancing, backed the "the stronger decisions being now taken by government and what we term as the "go now, go hard and go smart" strategy".
"Stay at home unless it is absolutely necessary that you go out", the prime minister told citizens. "We will be using all of those devices to get that message out but I think it's pretty clear that most people, if not every person in this country".