"Weddings can continue to be conducted where it is just the couple, the celebrant and the witnesses, that's no more than five people", he said.
However, exceptions would be made for aid workers and for compassionate, work-related and other essential travel, he said.
"Funerals are to [be] no more than ten persons, observing the four-square metre rules and social distancing practices".
Scott Morrison said it had "been a very hard decision" to prevent large weddings and funerals from taking place.
Australian Prime Minister Scott Morrison announced an outright ban on all overseas travel for Australians late Tuesday amid a raft of new restrictions created to slow the spread of the new coronavirus.
Funerals are limited to no more than 10 people.
Morrison acknowledged that New South Wales and Victoria - which pushed for more extensive restrictions - were "far more advanced" than other states in terms of case numbers, but despite not all states being in the same position, the cabinet had still achieved "consistency of application".
Australia has already ordered pubs to close and restricted restaurants and cafes to offering takeaway services in a bid to limit social gatherings.
The federal government will use biosecurity powers to prevent a small number of people who continue to ignore the travel warning from heading overseas from Wednesday. "But we need to put that arrangement in place".
Morrison said the reason for this additional rule is due to Australians still seeking to go overseas on holiday.
"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".
"The direction is being worked on overnight, a soon as that direction is signed off by the health minister, it will come into force then and that will happen tomorrow".
"Australians who have lost hours, lost work, businesses that have been forced to close businesses, these are heart-breaking events in our nation's history and story".
The operation of schools has been a flashpoint, with Mr Morrison advising that they remain open, while some state leaders urged parents to keep their children home. Be very careful. Because that would need to be sustained for a very long time.
"These are not things we can do now", the Prime Minister declared on Tuesday night when he told the country the lockdown will apply to weddings, funerals, food courts and much more from Wednesday night..
Chief Medical Officer Brendan Murphy said he was very anxious about the "very, very steep growth" in the rate of infections and urged people to change their behavior. I had hoped that would have been fully complied with and I've got to say, Australians have been pretty good about it.