Environment Minister Nick Smith is not 'sleeping easy” despite five days of clear weather lying ahead for salvors pumping oil from the Rena shipwreck.

Speaking at a press conference in Tauranga today, he spoke about the need to maximise the opportunity this good weather presented.

Environment Minister Nick Smith.

'I will not be sleeping easy until every last bit of oil is off the Rena.”

Salvage teams are again pumping oil from the vessel and are installing a second booster pump after the first failed today.

Maritime New Zealand salvage unit manager Bruce Anderson says the pumping began at 12.09pm and has continued since – with or without the booster pump.

'While ramping up the amount of oil being pumped it blew its circuits.”

The salvors' second, and only other, booster pump is being installed to help the Archimedes pump increase its present 4-5 tonnes per hour pumping rate.

'We will need a 10 tonnes per hour rate to be more confident.”

The pumps have to push the oil, which has a Marmite-like consistency, along a 160m pipe from Rena's fuel tanks to the Awanuia barge, anchored at the container ship's stern.

Rena remains afloat and in one piece despite significant cracking down both its port and starboard sides.

Bruce says the ship's stern section is remaining afloat in large part due to buoyancy created by internal air pockets.

A significant air pocket is in the ship's engine room, but the door to this is leaking.

Divers are working in a debris filled long corridor to seal the leak to this room with putty.

Most of the containers on the stern part of the ship are empty.

No more containers have fallen from the ship, with 49 of the 88 to have gone into the sea accounted for.

Salvage operations for these containers are being passed from the ship's salvor, Svitzer, to Braemar Howells.