UPDATE: UP TO 300 containers may have been lost overnight from wrecked ship Rena after it broke in two off NZ's Tauranga coast.
The Rena is now in two pieces, 20 to 30 metres apart on Astrolabe Reef, after it was battered by seven metre swells.
Between 200-300 containers are estimated to have been lost overnight yesterday, which are creating hazards for ships in the area, authorities say.
Port of Tauranga chief executive Mark Cairns says ships awaiting entry to the port should drift north of Mayor Island, because anchorages are likely to be affected by floating containers and debris.
Containers have been spotted 8-10 nautical miles north of the port.
Ships arriving and departing the port needed to exercise extreme caution and maintain a vigilant lookout, Mr Cairns said.
The port is monitoring channels with sonar and other methods.
The Bay of Plenty Regional Council has established a cautionary area around the ship, including Waihi Beach, Mayor Island and Maketu.
All vessels need to navigate with extreme caution, because the debris is unpredictable and could travel a long way, the council says.
The council has not extended the three nautical mile exclusion zone around Rena, but this will be reviewed as more is known about Rena's condition.
Maritime New Zealand (MNZ) salvage unit manager David Billington said the two sections of Rena remained on the reef, but the ship was badly damaged.
There had not been a significant leak of oil from Rena but trained oil-spill response and wildlife experts were preparing for the likelihood of more oil coming ashore, MNZ national on-scene commander Alex van Wijngaarden said.
Debris from containers is also expected to wash up.
The bad weather is expected to ease over the next three to four days.