Swimmers, surfers and boat users are being warned to be careful as more containers and debris from the Rena are being sighted in the Bay of Plenty waters.

Severe weather with swells of up to 6m has overnight pushed more containers off the cargo ship wrecked on Astrolabe Reef, about 25km off the coast of Tauranga.

A container from Rena that washed up on Marine Parade during the first storm the ship encountered on October 12.

The ship is now in two pieces with the forward and aft sections of the ship now 30 metres apart.

Maritime New Zealand spokesperson Bruce Fraser says at this stage they do not know exactly how many containers have been lost overboard.

Floating containers are being located to the northwest of the ship, and a large amount of debris is also being sighted downwind of the vessel.

With the wind expected to change from southeast to 25knot northeasterlies today more debris and containers are expected to wash ashore this afternoon.

Navigational warnings are being issued to shipping and boat users as the ship continues to be battered by strong swells.

In response to the change in situation of the Rena, the Bay of Plenty Regional Council is issuing new warnings to anyone travelling by boat in the area.

Bay of Plenty Regional Council Water Management Group manager Eddie Grogan says council is currently re-assessing the maritime exclusion zone around the Rena.

'We will provide more information once we've assessed the situation, however we anticipate the exclusion zone will be increased.”

He says while conditions might be good for surfers, people should be aware that a large amount of debris is in the water.

This includes timber, bags of milk powder and containers.

'We're asking people to be conscious of the hazards and to be sensible and careful.

'Personal safety is our top priority so we're asking people to not put themselves in situations where they could get injured.”

Bay of Plenty Regional Council staff are continuing to work with Maritime New Zealand and Braemar Howells in maintaining safe navigation channels.

It is important to notify Maritime New Zealand immediately if you see oil or containers in the water, by calling 0800 645 774.

Anyone found in the exclusion zone without the express permission of the harbourmaster may be fined $200 or prosecuted.