The measures put in place to stem the seeding of the Covid-19 Omicron variant were to end at 6am on Wednesday, NSW Health announced late on Tuesday.
Instead, fully vaccinated people arriving from South Africa, Lesotho, Zimbabwe, Botswana, Mozambique, Namibia, Eswatini and Malawi must self-isolate for 72 hours and can leave after receiving a negative test.
They must also avoid high-risk settings for seven days.
People who have previously arrived from those countries and were in hotel quarantine must remain there until at least 72 hours after their arrival in the state, NSW Health said.
Unvaccinated travellers would still be required to enter quarantine for 14 days.
It brings all international arrivals into the state under the same testing and isolation requirements.
People flying into New South Wales from the eight nations were previously ordered into 14 days of isolation under rules introduced in late November.
The measures were put in place soon after Omicron was detected in South Africa and declared a new variant of concern by the World Health Organization.
On Tuesday NSW recorded 804 Covid-19 cases, the most seen in the state for 10 weeks.
Chief Health Officer Dr Kerry Chant "strongly encouraged" all international arrivals to get tested 12 days after arrival.
"With the festive season upon us and people starting to gather in larger numbers, I urge everyone to maintain their vigilance and to continue to come forward for testing with even the slightest symptoms and to follow the public health advice," Chant said.
So far 85 cases of the Omicron variant have been identified in NSW, with some believed to have contributed to a series of large clusters seeded at pubs and nightclubs.
One outbreak stemming from a Newcastle nightclub on 8 December has led to more than 200 infections, including confirmed cases of the Omicron strain.