Northern Territory water police have battled a two-metre swell and rough and stormy wet season conditions to rescue a sailor who fell ill on a Japanese tanker offshore from Darwin.

Key points: Police had to undertake the evacuation outside the safety of Darwin Harbour

Police had to undertake the evacuation outside the safety of Darwin Harbour The Filipino man had fallen ill from abdominal pains while onboard the Japanese LNG tanker

The Filipino man had fallen ill from abdominal pains while onboard the Japanese LNG tanker He was in the care of paramedics in Darwin by the evening, just hours after the dramatic rescue

Two water police officers, together with a St John ambulance paramedic, were called out to the 300-metre LNG taker on Sunday afternoon, in the Timor Sea, after reports of a Philippine national having been hit with severe abdominal pain onboard.

Due to the urgency of the situation, the evacuation was forced to take place outside the shelter of Darwin Harbour, and an onboard crane had to be used to help winch the patient onto the police boat.

The Pacific Breeze was bound for Darwin when disaster struck. ( Supplied: NT Police )

The retrieval was pulled off within two hours, with NT Police lauding the operation's success.

"We were dealing with a two-metre swell and thunderstorm conditions with a storm warning for the area," Sergeant Andrew Hocking said.

"Time was going against us but we managed to outrun the storm on the way out, get the male safely on board, and push through it on the way back to shore."

The patient was transferred to paramedics at 6:30pm.