Just two containers are confirmed to have fallen into the water from the Rena as the wrecked vessel's stern section slipped down the Astrolabe Reef this morning.

The ship section began its descent at about 8.30am with it sliding down the reef, leaving most of it submerged.

It is lying on the reef at an angle of about 27 degrees.

Rena's stern is mostly submerged on the Astrolabe Reef. See Maritime New Zealand video footage of the Rena wreck site below.

The bow section remains on the surface in about the same position as it was on October 5 when the ship ran aground.

Container salvage contractor Braemar Howells is reporting just two containers have fallen from the wreck today with one sinking at the reef and the other floating away.

The total number of containers to fall from the wreck since the Saturday storm that broke Rena into two pieces is still unknown, but is estimated to be about 150.

Braemar Howells spokesperson Claudine Sharp says 49 containers are confirmed to be floating with the contents of 45 of these identified.

There are also 29 confirmed beached or ashore from Matakana Island north to Waihi Beach.

Claudine says the contents of the identified containers are not legally considered hazardous materials and include cargo such as timber, paper, milk powder and some plastics.

The remaining containers to have fallen into the sea since the Saturday storm are believed to have sunk at the reef.

Braemar Howells is working to remove the containers from the sea before they wash ashore.

'Our plan is still essentially a marine operation, but the weather makes it difficult to pick them up,” says Claudine.

Svitzer is the ship salvage company working on the Rena wreck and its salvage manager, Paul van ‘tHof, says there are about 400 containers in the now submerged stern section.

He hopes salvors can recommence container lifting operations from the stern section using the Smit Borneo barge once the weather settles.

This will also depend on the stability of the submerged section of the ship.

'We believe at the moment it is settled, but we are not sure how stable it is,” says Paul.

Weather is not forecast to improve until Saturday and assessments need to be made about whether the Smit Borneo crane barge can be safely positioned near the submerged stern.

At this stage the sea condition is not permitting this assessment, nor is it possible to conduct underwater assessments about the stability of the stern section.

The bow is fixed hard to the reef and following the stern's sinking a Svitzer chartered helicopter landed on the bow to assess its stability.

Paul was on that flight and he said while movement on the bow was noticeable it was not more than was experienced prior to the 236m container ship's separation.

The ship's separation today has released more oil into the sea, however, Maritime New Zealand national on scene commander Alex van Wijngaarden says the amount is small.

While hundreds of tonnes of oil was released into the sea in October last year, only a single digit's worth of tonnes is believed to have leaked into the sea today.

MNZ's trajectory modeling shows the oil is heading south and is expected to first wash ashore at Motiti Island at about 6pm and then on the mainland between Maketu and Matata on Wednesday afternoon.

Special attention is being given to some areas anticipated to be affected.

'We are implementing booming plans for sensitive areas,” says Alex.

Where oil washes ashore, Alex is urging the public to keep clear to allow the trained teams to undertake the work.

'This needs to be done in a coordinated move to prevent things from getting worse than they are.”

In addition, he says Svitzer has deployed some on-water oil control measures at the site of the wreck.

Environment Minister Nick Smith is in Tauranga and speaking at a press conference he commented on how he was pleased with the clean-up effort over the last two days.

He says the government's goal is clear.

'The Rena is in its death throes and the government priority is about minimising the harm to the environment.”

He visited Waihi Beach today, where 12 containers have washed ashore, and with four already removed from the beach says work there is proficient.