Hundreds of tons of oil have leaked from the Liberian-registered container ship Rena, which ran aground on a reef last Wednesday.
With beaches coated black and some seabirds already stricken, the accident is now the country's "worst maritime environmental disaster," the New Zealand government announced Monday.
Bad weather has hindered efforts to reach the ship, which lies stranded about 14 miles (22 kilometers) offshore, said Catherine Taylor, director of the government body Maritime New Zealand, according to the New Zealand Herald.
"We are at the mercy of the sea," Taylor said. "It is not a quick fix."