Authorities in New Zealand say salvage crews working to off-load more than 1,000 tons of oil from a grounded container ship have again suspended operations due to bad weather.

The government agency Maritime New Zealand said Tuesday the stranded cargo ship, which ran aground nearly two weeks ago, was pounded by heavy seas and 65-kilometer an hour winds overnight, forcing salvage crews to stop work.

Authorities said Monday that the crippled Liberian-flagged Rena still holds at least 1,300 tons of oil in its tanks.

Hundreds of volunteers are helping to clean up beaches in the Bay of Plenty, and restore surviving sea birds to health. Officials said 1,300 birds have so far died in the pollution.