Major environmental accident in the UK: around 200 barrels of oil leaked from the Wytch Farm pipeline in Purbecks and spilled into Poole harbour.
The UK's Health Safety Agency has declared a state of emergency and banned bathing until further notice.
The local media reported it.
The plant is owned by Perenco, who confirmed a "limited oil leak" and ensured that the leak has been blocked.
A "comprehensive investigation" has been launched into what happened.
Cleaning operations are in progress.
Wytch Farm, operational since 1979, is one of the largest onshore oil fields in Europe.