Salvage crews have removed four containers of dangerous goods from the bow of the broken ship Rena.

Maritime New Zealand said the containers removed yesterday held empty tanks that were formerly used to store hydrogen peroxide.

Most of the chemical had escaped from the tanks - though residual traces remained, MNZ said.

Cargo recovery company Braemer Howells would use special procedures to process the dangerous goods when they were brought ashore.

Salvors have now recovered 43 containers from the Rena since it broke in two earlier this month.

About 400 containers are still in the mostly submerged stern section of the ship.

It was intially thought there were 11 containers of dangerous goods on board the Rena when it crashed on Astrolabe Reef off Tauranga.

Insurers acting for the Mediterranean Shipping Company, which chartered the vessel, revealed an extra 21 containers containing a dangerous substance known as cryolite in November.

- Herald Online staff