From midnight Tuesday, police and Defence Force personnel had begun patrolling the NSW and Victorian border, as it slammed shut for the first time in a century.
Community transmission of COVID-19 continued to rise in Victoria as it recorded 191 cases, the biggest daily increase since the pandemic began. There were 127 new cases were on Monday, and 74 on Sunday.
Hours before the rules were due to come into effect, the details were still being worked through.
We've taken a look at everything we know about the border closure and how it could affect you.
What are the rules and why now?
From midnight on Tuesday the border between Victoria and NSW shut, and was expected to remain closed for several weeks.
NSW Police are enforcing the closure at more than 50 crossings and using drones at river crossings, should anyone attempt to swim across.
Victorians will not be allowed to enter NSW unless given an exemption. Some workers including freight drivers and emergency service workers will be among that group.
These rules also apply to Victorians who attempt to enter the ACT.
Those who are given a permit to enter NSW or the ACT will need to self-isolate for 14 days.
NSW Premier Gladys Berejiklian said it was a step the government had to take to protect the health of the community as community transmission of coronavirus in Victoria soared.
Victoria recorded its biggest daily increase in COVID-19 cases on Tuesday with 191 new infections.
The majority of active cases in the state are from community transmission. Metropolitan Melbourne will return to lockdown from Wednesday night, while nine public housing blocks remain in 'hard lockdown'.
NSW Chief Health Officer Kerry Chant said she advised the closure due to the increase of cases outside those hotspots.
"There is often a lag between when cases are recognised and diagnosed," she said.
"We needed to get ahead of the potential spread to safeguard the seeding of NSW.
Who can get a permit and where do I apply?
Applications for a permit to cross the NSW and Victoria border can be accessed via Services NSW.
Applicants who meet the criteria will be processed automatically, more complex applications will be reviewed by NSW Health.
Eligible people include NSW residents returning home, cross-border residents, boarding school students, carers and critical workers such as freight drivers.
Anyone transiting through NSW to another state or territory, entering for child care arrangements or compassionate grounds are also eligible.
People do not need a permit to cross if they are emergency or medical services, attending court or escaping a risk of harm.
Permits are valid 14 days and apply to all border crossings.
Police Commissioner Mick Fuller expected huge delays at main crossings as authorities determined who would be granted exemptions.
"I ask if anyone has a high level need because of medical reasons, then they need to throw their hands up so police can address that and assist them through quicker," Commissioner Fuller said.
"If people could just be patient over the next 72 hours and not cross until you really have to."
Border communities such as Albury/Wodonga and Echuca/Moama "will be seen differently" to other postcodes.
Mr Fuller said it would be easier for those residents to cross and it was likely they would only require one permit for the duration of the closure.
Ms Berejiklian urged patience from the community and said it was going to be very difficult for two or three days.
"Some people, who normally travel across the border as their daily lives, will be restrained until we get the permit system in place," she said.
What do I do if I'm not in my home state?
NSW residents in Victoria, and Victorians currently in NSW will need to apply for a permit to return home.
Residents returning to their home state, including transiting through NSW, are eligible for a permit.
However, if you are a NSW resident coming from Victoria you will be required to undergo 14 days self-isolation.
Victorians returning from NSW do not have to self-isolate but anyone living in metropolitan Melbourne or Mitchell Shire will be back under stage three lockdown rules.
What if I had booked a flight or holiday?
Unfortunately, you will most likely need to cancel any upcoming interstate travel you had booked.
Virgin Australia has waived change fees for bookings made between April 21 and September 30 for passengers who want to change their booking or can no longer travel.
Qantas said it would only operate limited flights to and from Melbourne for essential travel for the rest of the month.
Qantas passengers on cancelled flights or who are not allowed to travel due to restrictions can get a refund or flight credit.
If the flight is still operating passengers can change without incurring a fee or receive credit.
How will the closure be enforced?
About 650 NSW police officers and 350 defence force personnel will be stationed at the 55 border crossings between NSW and Victoria.
Police can hand out on-the-spot fines of $1000 for those not complying with the new directions.
Crossing the border illegally or falsifying information for exemption could attract an $11,000 fine or six months' imprisonment.
The most police resources will be deployed at five primary crossings including the Hume Highway, Cobb Highway, Princes Highway and Sturt Highway.
The 29 less frequented crossings will also be patrolled.
A further 20 tracks will be watched over by drones and aircraft.