The leak has come from the Wytch Farm facility in the Purbecks which is one of the largest onshore oil fields in Europe.
Philip Broadhead, the leader of Bournemouth, Christchurch and Poole Council, has said oil has escaped into the water and surrounding area.
Mr Broadhead added in a statement: “As leader of the council I will, along with the senior council team, be working to see what implications this leak may have and what action we may need to take.
“It is of course extremely disappointing to hear of this event, and while there will be a time later for anger and investigation, our focus now must be on ensuring we can mitigate any impacts of this situation.”
The UK Health Security Agency in the South West has said members of the public should not swim in Poole Harbour or the surrounding area until further notice.
Their statement continues: “Anyone who has come into contact with the spill should wash immediately with soap and water.
“If eyes have come into contact with the spill, they should be rinsed with water.”
Dorset Police has said the incident is being “overseen by a number of local agencies”.
Their statement continues: “Please follow the advice not to swim in Poole Harbour or the surrounding area until further notice.”
The Wytch Farm facility, taken over by Perenco in 2011, was previously operated by BP.
The major incident was declared after about 200 barrels of reservoir fluid including *OIL* leaked into the water at Poole Harbour in Dorset. The Dorset Coast already faces an ecological emergency from raw sewage dumping by Wessex Water
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