The 800kg haul was discovered following a joint operation between the Royal Gibraltar Police and HM Customs marine officers and the Guardia Civil late last night.
Acting on information that up to five large Rigid Hulled Inflatable Boats (RHIBs) were operating in area of the straits and waters surrounding Gibraltar, marine assets of both law enforcement agencies carried out patrols.
These culminated in two high speed pursuits which saw the offending vessels move out of British Gibraltar Territorial Waters (BGTW).
During the second pursuit which occurred at around 5:40 this morning, the vessel began offloading the drugs into the water and fled into Spanish waters.
Some 27 bales with a street value of £4,050,000 were later retrieved from the water.