Maritime New Zealand says fuel oil that spilled from the stricken container ship Rena on Saturday night may reach Coromandel by the weekend.
Four vessels using booms were sent to collect the five to ten tonnes of oil that escaped from the ship at the weekend.
Maritime New Zealand's on-scene commander Rob Service says the remaining oil has broken up and is generally heading north.
He says small amounts could reach Mayor Island and potentially Coromandel Peninsula this weekend, depending on the weather and tidal movement.
The agency also announced that 645 tonnes of oil has now been pumped off the ship, just under half the oil believed to be on the ship when it grounded on Astrolabe Reef near Tauranga on 5 October.
The authority says oil is now being pumped from the ship's settling tanks into the number five port fuel tank where it will then be transferred onto the bunker barge Awanuia.
Earlier, Svitzer Salvage spokesperson Matthew Watson told Morning Report the salvors have been making "steady and sure-footed" progress in favourable weather.
Mr Watson says the salvage teams are working on the port side tank, which originally contained 772 tonnes of oil.
They are also considering how to remove oil from the other four tanks on the ship.
Fine, calm conditions are expected to continue until at least Thursday.
No oil on Mayor Island
A Department of Conservation team that went to check on the impact of the weekend's oil spill on Mayor Island has not found any contamination but did recover two birds covered in oil.
Team members went to the island on Monday and have since been combing the coast for any signs of oil.
Kerri Morgan of the Oiled Wildlife Response Centre says it appears the two birds had flown back to the island after being coated with oil at sea.
A shoreline stabilisation site has been set up at Mayor Island, so any oil-affected wildlife found can be treated.
Mayor Island is in a marine reserve and is considered a biodiversity hotspot.
Meanwhile, about 1370 dead birds have been recovered since the Rena began leaking oil almost three weeks ago.
Another container found
Maritime New Zealand says a container from the Rena has washed up near Opotiki in Eastern Bay of Plenty.
Just 12 of the 88 containers that fell off the ship during rough weather two weeks ago have so far been recovered.
The whereabouts of 35 other containers are known and the rest are unaccounted for.
Maritime New Zealand spokesperson Steve Jones says the container near Opotiki is believed to have come ashore at a difficult place to get to.