The spill is potentially very serious

Local environmentalist

Eighteen tonnes of rat poison pellets and a small amount of paint tipped into the sea when a lorry and trailer overturned on a narrow coastal highway at the Kaikoura coast, 200km (125 miles) from Christchurch.

About 400 square metres of the sea turned bright green.

It was unclear whether the brodifacoum rat poison pellets or the green paint was to blame.

The authorities are monitoring the area which is home to large numbers of marine mammals. Most at risk are fur seals and birds, officials said.

Tourists from all over the world visit Kaikoura, which has the draw of whales feeding near the shore.

There are fears for marine life

"The spill is potentially very serious," Bob Simpson of Environment Canterbury told Television New Zealand.

"We have been on site all day and will remain until we ensure the environmental effects are minimised."

Officials have warned the fishing industry to avoid the area, and a temporary ban has also been placed on fish and shellfish by the Kaikoura District Council.

Locals rally round

Local people rallied around to help during the clean-up.

The ocean is very important to almost everyone that lives up there so... people offer to help in any way

Local volunteer

"We've offered our boats and I think others have as well," Kaikoura Whalewatch manager Wally Stone told the New Zealand Herald.

"The ocean is very important to almost everyone that lives up there so something like this means people offer to help in any way they can."

Health officials hope the slow-release characteristics of the poison will prevent serious harm to wildlife.

Although there is no threat to humans from the poison, local health authorities have said anyone showing symptoms of sore skin or vomiting should go to the hospital, the Herald reported.