Personnel from Maritime New Zealand and Svitzer Salvage have been airborne to monitor the slow progression of the stern into the sea since the vessel's status began to change rapidly after 8.30am today.
Tauranga Mayor Stuart Crosby said he had been warned there was a "strong possibility'' the stern would sink, so the news had not come as a shock.
"There is a small concern about whether it will settle on the sea bed and if this will create extra debris or if this will aid in the possible recovery of the Rena.''
Mr Crosby said his personal view was that the sinking of the stern was positive as it was off the reef.
"If it's in reasonably deep water it could become a diving attraction. This is just another step in the Rena saga that would eventually happen. Maybe out of sight out of mind but this could be a positive thing for us.''
Tauranga MP Simon Bridges said there was a "sense of inevitability'' that part of the Rena had sunk.
"Sadly I wasn't surprised but in some way there is a silver lining because we now have a certainty about what's going on because it will sink,'' Mr Bridges said.
"We're not left wondering what might go on and now this has provided clarity for Maritime NZ and the salvors.''
Ngati Ranginui chairman Hui Kakahu Kaue told the Bay of Plenty Times yesterday there were spiritual, cultural, physical and emotional implications for iwi should part of the Rena sink.
"Physically, in terms of food we suffer, especially those in Motiti [Island]. There will be a long-term disadvantage and effect on them.''
Steve Penn, of the Waikato and Bay of Plenty Marine Recreational Fishers Association, said most fishers had accepted it was likely that the ship would sink.
He said he not believe the sunken hull would have a negative effect on the environment.
He did not think it would be much different to incidents in which battleships were deliberately sunk for fishing and diving purposes.
"Probably a lot of fishermen will say `great, a little bit more hapuka'. It could be a good thing,'' Mr Penn said.
"Depending on the depth, it will probably be an opportunity for divers.''
The ship would inevitably break down over the years.
Russ Hawkins of Fat Boy Charters said there could be some positive outcomes from the stern being sunk.
The eventual outcome could be of huge benefit for the local marine industry.
"Especially at this time of year. This is a special time of year, where you get the whole food chain out there from kahawai to trevally, kingfish, and marlin and sharks,'' Mr Hawkins said.
The sunken Rena could provide a boost to tourism, he said.
Hope wreck could be used for diving
Papamoa Surf Life Saving Club head lifeguard Shaun Smith, who has been looking at the Rena everyday since it ran aground, said the broken part of the stern was still sticking out at about a 45-degree angle.
"The bit of the front half of the boat is still sitting there perfectly and the second half has definitely sunk, but there's a big hunk of it still sticking out of the water.''
With the wind blowing directly onto the beach, Mr Smith was concerned further containers and debris could come ashore.
There had been earlier discussion over whether the stern would be left where it was or brought back to the surface and removed if it sank.
Green Party MP and oceans spokesman Gareth Hughes said people would have the opportunity to dive to the wreck if it was left where it was.
In its current position, the stern would sink to a depth of about 90m, meaning divers would be able to reach it. Most divers can go to only half that depth.
"Although it would have been ideal if it the stern could have been towed in and cleaned first, the salvors said it wasn't safe to bring it in. Safety has to be paramount and we have to defer to the experts,'' he said.
Sinking closely monitored
Maritime New Zealand confirmed this morning there has been change in the position of the ship's stern and they are closely monitoring the situation.
A Maritime spokeperson said the accommodation section of the Rena was already completely underwater.
There was no one on board.
"The accommodation section, the white part that sticks up, is beneath the water. The front of the aft part of the ship is still above water and it's still upright at this stage,'' the spokeswoman said.
The aft section is the larger part of the stricken cargo ship, which ran aground on the Astrolabe reef off Tauranga in October.
Salvors noticed the stern moving on the reef about 9am.
MNZ staff and salvors Svitzer have been airborne to monitor the slow progression of the aft section into the sea since the vessel's status began to change rapidly after 8.30am.
Information about any further release of oil, debris or containers from the Rena would be released as soon as it was available, MNZ said.
Transport Minister Gerry Brownlee is heading to Tauranga and will hold a press conference at 3pm.
Papamoa Surf Life Saving Club head lifeguard Shaun Smith, who has been looking at the Rena everyday since it ran aground, said the broken part of the stern was still sticking out at about a 45-degree angle.
"The bit of the front half of the boat is still sitting there perfectly and the second half has definitely sunk, but there's a big hunk of it still sticking out of the water.''
With the wind blowing directly onto the beach, Mr Smith was concerned further containers and debris could come ashore.
There had been earlier discussion over whether the stern would be left where it was or brought back to the surface and removed if it sank.
Green Party MP and oceans spokesman Gareth Hughes said people would have the opportunity to dive to the wreck if it was left where it was.
In its current position, the stern would sink to a depth of about 90m, meaning divers would be able to reach it. Most divers can go to only half that depth.
"Although it would have been ideal if it the stern could have been towed in and cleaned first, the salvors said it wasn't safe to bring it in. Safety has to be paramount and we have to defer to the experts,'' he said.
Meanwhile containers and debris from the wrecked Rena could drift as far north as holiday hotspot Whitianga and beachgoers have been warned to look out for timber and other dangerous material that could be hidden in the surf.
Mt Maunganui and Papamoa were yesterday spared the worst of the Rena breaking in two, but several freight containers and hundreds of 20kg bags of milk powder washed up on Waihi Beach - nearly 60km away.
There were also reports of looting of the stranded goods, tyres beaching at Matakana Island and a 3km sheen of oil stretching from the ship which is close to sinking since crashing into the Astrolabe Reef on October 5.
An observation flight this morning found more debris has been found around the Rena, including bits of plastic and wood.
Waihi Beach residents and holidaymakers awoke to fine weather yesterday and a number of containers and hundreds of bags of milk powder that littered the coast for hundreds of metres.
Gerard North, visiting from Dunedin, was looking forward to his first swim of "a really crappy summer" before fire firefighters cleared him and dozens of others from the popular beach.
"It's the best day we've had in ages and this is what we get - milk powder, containers and no beach," he said.
"It's bad, the milk powder stinks ... it's been a really crappy summer."
The beach was closed for some hours yesterday morning as decontamination crews converged and police reported receiving calls about a group taking bags of what appeared to be milk powder.
Twelve containers have now washed up on Waihi Beach, and another 25 have made landfall at Matakana Island.
Sergeant Dave Litton of Waihi police urged people not to take anything from the containers. He appealed to the group who took the goods to return them to the beach, where they can be managed by the clean-up crews.
Waihi Beach was reopened in the afternoon but people were cautioned about swimming and the area around containers and debris will be restricted if necessary.
Claudine Sharp, of recovery specialist Braemar Howells, said initial estimates of up to 300 containers being washed overboard on Saturday night were incorrect and based on photographs it was now calculated that about 150 were drifting in the sea.
By yesterday afternoon, 12 containers had come ashore between Waihi Beach, Bowentown and Matakana Island with timber, recycled paper and polypropylene ropes among the cargo.
A further 20 containers with the toxic substance cryolite had also spilled overboard but were likely to be in water surrounding the ship, because of the heavy weight of the cargo.
Cryolite is a by-product of the aluminium smelting process, which is considered low risk unless ingested or inhaled directly in its dry powdered form.
Experts say the cryolite on board Rena is low risk, given that it is only slightly soluble in water, and is expected to dissolve slowly.
Ms Sharp said the recovery teams were battling against the weather, but based on trajectory models debris would continue to wash up around Waihi Beach and possibly as far as Whitianga, about 160km north in the Coromandel Peninsula.
The Herald understands some debris was spotted off Whiritoa Beach, south of Whangamata yesterday.
"Our main plan for recovery is through our marine assets. We want to retain this through the ocean ... we prefer not to have them come ashore," said Ms Sharp.
"We are trying to trawl the debris where we can and reclaim the debris and try to keep the containers off the land."
Transport Minister Gerry Brownlee said the debris in the wrong circumstances could be difficult to deal with.
"Imagine loose lengths of timber sloshing about inside the surf alongside large sheets of plywood, it could be quite damaging for people who get in the road of it.
"So the advice that people should stay away from that debris, I think is advice that should be well-heeded."
Maritime New Zealand also reported small oil spills at Matakana Island, Mount Maunganui and Leisure Island after earlier reports of a 3km long sheen of oil that was about 10 metres wide leaking from the ship.
Maritime New Zealand salvage expert Jon Watson said there was still oil trapped in the vessel but authorities did not know how much and could not measure it.
Mr Watson said the Rena's stern section, which has listed to starboard by a further one to two degrees, was pivoting around a particular point on the Astrolabe Reef.
He said it was unclear how far it was from the reef's edge or what it would take to knock it off .
"We don't know what strength that point is on the reef. It may be a small bit of movement may knock it over."
Mr Watson said the ship will still be salvaged if it sinks, along with the containers that have sunk.
Maritime New Zealand salvage unit manager Dave Billington said salvors landed on the front section of the ship on Sunday but could not board the stern section as the salvage master deemed it too dangerous.
It was "highly likely" the remaining containers on the vessel would spill if the ship sank.
"The hatch covers are removed, if the ship does sink and turn upside down the containers will discharge from the ship," he said.
Maritime New Zealand national on-scene commander Alex Van Wijngaarden said there were reports of five oiled penguins, but investigations showed that just two were affected.
