"It was simply a matter of time before there would be a storm event of sufficient magnitude to break the vessel in two and what has transpired in the last 24 hours is very much expected," said Mr Smith.
He said things had improved from an environmental perspective with the removal of the bulk of the 1300 tonnes of oil on board which means "the risks for the environment are a fraction of what they were in October".
"It is possible that there will be releases of oil but they will be in the order of tens of tonnes and not hundreds of tonnes and those things are unlikely to result in any beach closures."
Mr Smith said the bow section of the vessel was firmly wedged on the reef and would probably not shift but the stern was "likely to sink at some stage" and recovery of the containers on it had become problematic.
"Certainly it is true that the potential for recovery of containers on the stern section of the vessel has now become an order of magnitude more difficult given the extent of the damage to the ship."
National On Scene Commander Alex van Wijngaarden said response teams including wildlife experts and defence forces had been mobilised.
He said trajectory modelling predicted any oil released from the ship was to have come ashore early this morning, landing on beaches south east of Mt Maunganui but this was weather-dependent.
Maritime New Zealand salvage unit manager David Billington said officials yesterday found the ship with many of its hatch covers broken and containers thrown into the sea.
He said salvors were working to assess its state so naval architects could undertake further calculations to get a clearer picture of its ongoing stability.
Mr Billington said more containers were likely to be lost.
Claudine Sharp of recovery company Braemar Howells said of the 837 containers on the ship before the weekend storm between 200 and 300 had been washed overboard.
Of those, between 20 and 30 per cent had been fitted with transponders and around 30 containers had already been found. Ms Sharp said just 20 per cent of the containers would float, the rest would sink.
Shipping lines to Tauranga harbour remain open but the three-nautical-mile exclusion zone around the Rena remains in place.
Ms Sharp said the company was working closely with the harbour master and had been doing sonar sweeps of the harbour entrance for invisible containers.
She said trajectory models showed containers and debris heading in a northwest direction, probably towards Waihi. The debris is likely to wash ashore this afternoon but this was again weather and wind dependent.
"Our plan is to corral them and recover them promptly."
Tauranga mayor Stuart Crosby said the inclement weather had kept people off the beaches.
He said people needed to leave debris washed ashore to the response teams.
"Kiwis are inquisitive by nature and I'm sure there will be a lot of people on the beaches looking for debris. The main thing is ... they don't touch it.
"The key issue has always been the oil, what oil that may have ended up on beaches will be very small and will be removed very quickly."
