Ships entering and departing the Port of Tauranga today are being escorted by a boat towing a sophisticated side scan sonar and magnetometer to detect containers in shipping channels.

Containers from the Rena wreck on Astrolabe Reef began washing ashore on Mount Maunganui beach last night, with four confirmed on the beach this morning.

A boat towing a sophisticated side scan sonar and magnetometer is escorting ships in and out of Port of Tauranga shipping channels, searching for containers from Rena.

Port of Tauranga chief executive officer Mark Cairns says cruise ships Volemdam and Golden Dawn will receive an escort into port today.

'It's good to see Volemdam turning and tying up, and we have got the Golden Dawn coming in. It's one bright spot in the whole disaster.”

'The launch is towing a really fancy sidescan sonar and magnetometer in the water and we are doing continuous scans with that, and escorting the vessels as they come in.

'So we are doing our best to keep things open.”

Mark says false reports the port might be forced to close are believed to have come from a misunderstanding of the navigational diversions announced by Maritime NZ.

Ships visiting the port are being diverted well away from the port's eastern approaches and closer to Mayor Island.

The port company's responsibility extends three nautical miles from the entrance, with the coastal waters navigation outside the port limits being the responsibility of the regional council and Maritime NZ.

'There were six vessels overnight and another six are planned for today,” says Mark.

Mark says the launch is working almost fulltime in the shipping channels and the port's Butters Group buoy maintenance section is also based at sea to remove any containers found in port approaches.

'We will be doing the continuous scan then when we have shipping coming in, they are being escorted in by a vessel with this sophisticated sonar being towed,” says Mark.

The exclusion zone declared east of Rabbit Island has closed the port's normal roadstead anchorage - where ships can wait to enter the port.

'We had to shift vessels last night from anchorages.”

A new roadstead anchorage area is expected to be past Karewa Island.