Concerns are growing about the potential environmental impact of the Sanchi oil tanker disaster in the East China Sea. Britain's National Oceanography Centre says pollution from the spill may be worse than expected. As Kate Parkinson reports -- the slick could spread much further and faster.

The worst oil tanker spill in decades in unfolding in the East China Sea. The Panama-registered Sanchi tanker was carrying nearly one million barrels of ultra-light crude Iranian oil when it sank earlier this month. Natural gas condensate has never before been spilled in such massive quantities before so there are a lot of unknowns.

KATYA POPOVA UK NATIONAL OCEANOGRAPHY CENTER "We don't really know how this spill will behave. It can mix with the water, it can evaporate, we don't know how much of this type of oil is there because we don't know how much was burned."

KATE PARKINSON SOUTHAMPTON "Led by Dr Popova, scientists here at the National Oceanography Centre have created an ocean simulation model showing the likely direction and range of the spill over the coming weeks."

This image from the simulation shows how the spill site sits among several ocean currents, including the powerful Kuroshio Current which runs alongside the coast of Japan. Strong ocean currents mean that an oil spill can spread rapidly over large distances and these maps show that pollution from the spill could spread much further and faster than previously thought. The team in Southampton believe that waters polluted by the Sanchi spill could reach Japan within a month, potentially impacting key fishing grounds and sensitive marine ecosystems.

KATYA POPOVA UK NATIONAL OCEANOGRAPHY CENTER "Even right now it's going over quite rich fishing grounds and then it has a potential to impact coral reefs and lots of marine protected areas around the Japanese coastline."

Condensate is toxic to aquatic life with long lasting effects and since the East China Sea is home to hundreds of species of commercially harvested fish as well as whales and seabirds, the Sanchi oil spill could have a huge environmental impact. Kate Parkinson, CGTN, Southampton.