As salvage crews raced to stop more oil seeping from the stricken Rena, which hit a reef last week, Mediterranean Shipping Co. (MCS) said the six sailors still in the country were staying at an undisclosed location.

The Philippine embassy said 19 of the 25-man crew had already flown home after being interviewed by New Zealand authorities over the disaster in the ecologically sensitive Bay of Plenty, which teems with wildlife.

Two of the remaining six -- the captain and second officer -- were charged this week over the October 5 accident. A Tauranga court ordered their identities be suppressed after lawyers raised concerns for their safety.

MSC, which had chartered the Rena, said there had been no direct threat to the sailors but that they were being kept in a secret location as a precaution.

"We're keeping them low key, at an undisclosed location," said shipping agent Mike Hodgins.

"We're not going to parade them in front of everyone in case some nutcase does something he shouldn't," he told AFP.

Hodgins said they were not under police protection and most people in the North Island community were taking a common-sense approach to the disaster that has blackened their beaches, although he had seen some anger toward the crew.

"I've been out in town and heard some people saying things, but it's just talk," he said.

Filipino community group Migrante Aotearoa New Zealand issued a statement headed "Filipinos appeal against racial hatred over Rena disaster" after one of its members, a parking attendant, was abused in an Auckland street.

"We don't want this to become a racial issue, Filipinos are as upset as anyone about this disaster... I hope this is an isolated incident," the group's coordinator Dennis Maga told AFP.

He said the Filipino community planned to organise a volunteer drive to help in the clean-up of affected beaches.

Tauranga mayor Stuart Crosby said frustrations over the accident should not be vented on the crew.

"In some respects that crew are victims as well, and I'd like to think that we'd be looking after them in a proper manner, as Kiwis should," he told TVNZ.

Maritime New Zealand (MNZ) said the slick, which has dumped clumps of oil on beaches, had thinned but was becoming wider. Whakatane, 90 kilometres (56 miles) east of Tauranga, is bracing to be hit.

A massive clean-up operation is under way along the coastline involving 1,000 people, MNZ said.

The government agency said 1,000 dead birds had been recovered and teams were trying to round up seals in the area. They had caught three so far.

Maritime salvage crews resumed a "highly risky" operation to try to pump remaining oil from the Rena, which is teetering precariously on the reef and threatening to spilt as huge cracks gape in its hull.

"The moment there is a sense that it may be too dangerous, or if anything changes, they will be getting back off that vessel quick smart," Matt Watson, whose company Svitzer is leading the salvage effort, told Radio New Zealand.

Up to 700 tonnes of oil has leaked from the vessel and salvage crews hope to drain the Rena's fuel tanks to stop all 1,700 tonnes it was carrying from spewing into the sea.

For more than a decade, the tourism industry has sold the country as "100 Percent Pure New Zealand" in an award-winning campaign leaning heavily on its natural beauty and clean environment.

Images of pristine beaches and frolicking whales and dolphins in the Bay of Plenty have featured prominently in the campaign, which Tourism New Zealand says "convey's everything fresh and unspoilt about the country and its people".

But the North Island bay's famed beaches have been left far from untainted this week after oil leaking from a container ship crippled on an offshore reef left stinking streaks of dark scum and hundreds of dead birds on the sand.

Compounding matters, the country's worst maritime pollution disaster has come while New Zealand is in the international spotlight as it hosts the Rugby World Cup, the largest event ever staged in the country.

"There's never a good time, but this is definitely not the best," said Tauranga mayor Stuart Crosby, whose city is the bay's largest tourist destination.

"We're in our premier visitor season... add to that the Rugby World Cup and a lot of media here, no, it's not good.

"But these things happen and we need to deal with it and get our beaches, harbours and estuaries cleaned up."

He said charter boat companies, accommodation providers and others involved in the industry would experience a slowdown as visitors shunned the area in the short term following the oil spill's "assault" on the local environment.

Crosby said the region also attracted more than 80 cruise ships a year and, while none had so far changed their itineraries, that lucrative business could also take a hit.

Vicky Mackintosh, owner of The Reef Hotel in Mount Maunganui, said many international tourists were now rethinking their travel plans.

"We're having emails as far away as Germany at the moment to say 'what's it going to be like at Christmas-time? Shall we cancel our booking?'," she said.

"So we can see a lot of people not wanting to come to Mount Maunganui for their holidays this year."

Steve Penn, president of the Mount Maunganui Fishing Club, said every aspect of the local economy relied to some extent on tourism, with 80,000 recreational anglers flocking to the area annually.

"We've already cancelled a major fishing competition, which was coming up in a fortnight, because of the danger of the flotsam out there and the possibility of hazards," he said.

Transport Minister Steven Joyce, who has been overseeing the oil spill response, also denied New Zealand's "brand" had been irreparably damaged.

"Obviously, it would have been better it if hadn't occurred... the reality is that this happens in the world from time to time, we're a maritime nation, we've had shipwrecks before, as have other countries," he said.

"We'll clean it up and make sure that it's put back the way it started.

"The fact that we do that, and the way that we do that will, if anything, over time underline the way we see our environment."