An ingenious thief swiped $236,000 on a flight in the Caribbean after sneaking into the cash-laden cargo hold via the toilet, police say.

A Brink's security employee placed three sacks of cash, containing a total 1.2 million euros ($1.65 million), in the hold of the Air Antilles plane before it headed from the French island of Guadeloupe to the Franco-Dutch island of Saint Martin.

The security guard took his seat on the plane but when the flight landed 40 minutes later it was discovered that 172,000 euros ($236,000) was missing from the sacks.

Police are seeking a man who complained he felt ill and spent most of the journey in the toilet. In fact, he was removing panels to gain access to the hold in the rear of the plane.

Shortly before landing, the unnamed man - who was travelling with a woman who appeared concerned about his health - asked a hostess for an ambulance to meet him on the tarmac, witnesses said.

When the ambulance arrived, the man said he felt suddenly better and walked out of the airport without having to go through the normal security checks and disappeared, police said.

Cleaners who found bundles of notes in the toilet raised the alarm.

The woman travelling with him was questioned in the baggage arrival hall but did not have any of the missing money.

- AFP