An oil sheen has been spotted on the surface of the water surrounding a stricken cargo ship near Tauranga Harbour.
Authorities have been assessing whether any oil has spilled from the 236m cargo vessel Rena, which struck the Astrolabe Reef, north of Motiti Island, around 2.20am.
An aerial flight this morning has identified a light oil sheen on the surface of the water near the ship, which was fully laden.
This has been assessed as hydraulic oil from the vessel's engine, and Maritime New Zealand says the fuel tanks are still intact.
There are no reported injuries to the 25 crew on board.
The vessel, which left Napier bound for Tauranga Port, is on a 10 degree list, but is stable on the reef.
Two of its cargo holds are flooded, and pumps are being used to extract the water.
"As a precautionary measure, fuel in tanks on the port side is being transferred to the starboard side," Maritime New Zealand said in a statement.
"The ship's captain is in discussion with the ship's owner and salvage experts to assess how best to move the ship off the reef - this is expected to take some time."
MNZ's Marine Pollution Response Service is mobilising its team of trained spill responders, as well as specialist equipment to the site.
Members of the National Oiled Wildlife Response Team are also on their way to Tauranga.
MNZ has also activated its Maritime Incident Response Team (MIRT), comprising technical maritime experts.
The team is monitoring the situation closely from Wellington and has a maritime safety inspector on board the vessel assessing the damage.
MPRS, in conjunction with the Bay of Plenty Regional Council, has coordinated the flight over the area this morning which spotted the oil sheen.
Vessels ordered to steer clear of stricken ship
Regional harbour master Carl Magazinovic has directed all unauthorised vessels to stay at least 1km clear of the reef and the grounded ship until further notice.
Mr Magazinovic said there were already reports of sightseeing vessels near the grounded ship, potentially causing safety issues and disrupting response efforts.
"This situation is expected to continue for some time so we will be monitoring movement of vessels around the area, and anyone found breaching the exclusion zone could face a fine of up to $20,000."
Maritime New Zealand has declared a tier 3 response, due to the size and complexity of the grounding, and is managing the operation through the Incident Command Centre established at Mount Maunganui.
Sightseers flock to waterfront
Bay of Plenty Times reporter Kiri Gillespie said weather conditions on the harbour this morning were hazy.
She said Maritime New Zealand vehicles are at the port and people are flocking to Omanu and Mount Maunganui Main Beach to try to see the vessel - but are being thwarted by the weather.
The Rena has had issues in the past; In August, the 22-year-old vessel was detained for a day in Freemantle, Western Australia, by the Australian Maritime Safety Authority after "serious deficiencies" were found on the ship.
The authority's report found the vessel had "not been maintained between surveys", the "hatchway cover securing arrangements defective" and cargo was not stowed and secured as stipulated in the cargo securing manual.
The vessel was released after these issues were addressed.