Clumps of oil have been found on Mount Maunganui beach in the Bay of Plenty.

Oil began leaking from the Rena, a Liberian-flagged vessel, after it struck the Astrolabe Reef, about 12 nautical miles off the coast of Tauranga, on the North Island, on Wednesday, creating a five-km (three-mile) slick.

Efforts to recover oil from the grounded ship, now heading south down the coast, are being hampered by high winds and strong swells.

Approximately 10 tonnes of fuel oil was transferred to tanks on board a barge before the recovery operation was suspended on Monday.

Almost all the 1,700 cubic metres (450,000 gallons) of fuel carried by the ship remained within the vessel's hull.

New Zealand's oil spill response agency, Maritime New Zealand (MNZ), is advising people to avoid the beach for health reasons.

CNN