Princess is cancelling sailings until 19 December and P&O Australia is extending its suspension of operations through to 17 December.
Guests booked on a cancelled Princess cruise will be moved to an equivalent sailing in 2022, or be offered a refund or future cruise credit.
The extension to P&O’s pause applies to cruises scheduled to depart from 17 September.
According to the line, the industry has been "discussing a framework" for the restart of domestic-only cruising with the government and public health authorities since last October.
Sture Myrmell, P&O Cruises Australia president, said: "These discussions have been under way for some time, and we look forward to the opportunity to agree a pathway for starting cruises that carry Australian residents on Australian itineraries.
"This is about the livelihoods of the thousands of individuals and small businesses, many of which are family-owned businesses, who rely on the cruise sector.
"These businesses cover a range of activities such as the supply of fresh food, entertainment, shore tours, coach operators and marine engineering services."
P&O guests whose bookings have been affected will be notified of the pause and options available either directly or via their appointed travel agent.