The first of more than 1200 shipping containers have been removed from the stricken cargo ship Rena, six weeks after it ran aground on the Astrolabe Reef off the coast of Tauranga.

Three containers were lifted off onto the crane barge Sea Tow 60 today, the start of a process expected to take several months.

Poor weather halted the operation yesterday, but salvors today made the most of good conditions in the Bay of Plenty, Maritime New Zealand salvage manager Kenny Crawford said.

"Obviously getting the first container off is a milestone for the operation, but there is still a very long way to go. The removal process will take time as, for safety reasons, each container needs to be lifted separately. Each will also present its own challenges, depending on its position on the vessel and how badly damaged it is.''

So far, 118 electronic transponders have been fitted to the containers sitting most precariously on deck, which will allow them to be tracked should they topple overboard.

A further 102 transponders are being prepared and fitted.

"We've also achieved another milestone in emptying port fuel tank number five, which can now be classified as empty of oil,'' Mr Crawford said.

Nineteen of the 88 containers that fell off the ship in bad weather last month have been recovered, but the other 56 are still unaccounted for.

Once recovered, the containers will be decontaminated and taken to port.

Meanwhile, beaches from Mount Main Beach to Maketu estuary were officially reopened to the public this morning, three days after salvors managed to pump the majority of oil off the ship.

National on scene commander Mick Courtnell said resources were still in place to respond to any further reports of oil.

Access restrictions remain in place at Papamoa and Maketu Spit and the public are advised to exercise caution.

- APNZ