Man rescued after jumping from oil tanker off Port Phillip Bay

A man will be placed in mandatory hotel quarantine after jumping from an international oil tanker in waters off Melbourne's Port Phillip Bay.

Water police rescued the Georgian national on Sunday night, after he allegedly climbed down a rope, into the water from the oil tanker Kanpur, docked in the bay.

The 31-year-old sailor was in the water, clinging to a navigational marker for an estimated 20 hours before the Airwing spotted him five kilometres from the dock near Point Cook about 7.50pm.

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Seafarers Victoria CEO Sue Dight said the man's plunge into the water may have been a desperate attempt to flee the vessel.

"He may have felt a desperation that put him in this situation where he couldn't stay aboard any longer," she said.

"It's not that uncommon, seafarers are getting desperate unfortunately because of their conditions."

A caller phoned into 3AW's Rumour File this morning and said the man had been travelling on the tanker for eight months before making his daring escape attempt.

The Mission to Seafarers will put together a care package for the man.

He was taken into custody by Australian Border Force before being transferred to a Williamstown hospital for observation.

He is expected to go into 14 days of quarantine once cleared by doctors.

Officers who came into contact with him will are also isolating as a precaution.