More than 20 containers have been removed from the stricken cargo ship Rena, but salvage operations are at risk with the weather forecast to deteriorate today.

Calm sea conditions in the last three days allowed salvors to remove a total of 23 containers from the stern of the ship, leaving 1257 containers still to be removed.

The barge Sea Tow 60 sits alongside Rena at Astrolabe Reef, ready for container removal.

However, the New Zealand MetService has issued a strong wind advisory for today with winds of up to 25 knots gusting to 35 knots this afternoon.

Moderate sea conditions are also expected to turn rough.

Maritime New Zealand Salvage Unit Manager Kenny Crawford says operations will continue as long as conditions remain favourable.

'Cranes cannot operate in winds greater than around 24 knots, so we are very much at the mercy of the weather. Even if it looks calm, strong winds can halt operations.”

Salvors have now fitted 220 transponders to containers aboard the Rena and tugs are on hand to provide additional support for vessel operations.

Containers recovered from the Rena are being transferred from the Sea Tow 60 on to the salvage support vessel Go Canopus, before being brought into Port of Tauranga for unloading.

Container processing is being carried out by Braemar Howells and containers that require cleaning and treatment will be taken to the waste transfer centre in Truman Lane.

Harrison's Cut will be used only for submerged or floating containers that cannot be recovered by barges and must be marshalled onto the beach for collection.

MNZ National On Scene Commander Mick Courtnell says clean-up teams have had a successful few days washing down rocky foreshores.

'Water blasting around the Mount is progressing well and teams have been out washing rocks by hand at Leisure Island. Mechanical cleaning is ongoing at Papamoa and Maketu and all restricted areas will be clearly signposted.”

Mick says there is still a risk of another release of oil as salvors continue to strip oil from the grounded Rena.

'The situation could unfold in any number of ways and we will continue to have teams and equipment ready to mobilise at a moment's notice.”