The crew of a large cargo ship headed for Sydney have been told to catch or kill a rogue monkey running loose aboard the vessel or they will not be allowed to dock.
A spokesman for the Australian Quarantine and Inspection Service said the container ship, said to be coming from China, was due in Australian waters within two days.
The ship's crew have sent Australian authorities photos of the animal in a bid to have it identified.
Although a spokesman said the shots were of a poor quality and showed only a "small brown blur", it was believed the monkey was a macaque.
The crew have no idea how the animal came to be aboard and say they have not been able to get close to it since first spotting it sitting on top of a container some weeks ago.
It has not been seen for almost three days.
The ship's captain has been advised of Australia's quarantine requirements and warned the monkey had to be captured or "appropriately disposed of" before the ship would be allowed to berth in Australia.
The AQIS spokesman said it "now appeared the animal was no longer a quarantine threat" as no droppings had been seen.
However, quarantine officers and a vet would board the ship if the monkey was not found to make their own inspection.
The ship would moor at a buoy out to sea while this was carried out.
If the monkey was still not found the ship - a large new container vessel - would probably be allowed to dock to unload, but it would a slow process as each contained would have to be kept under surveillance as it was moved and unloaded.
Quarantine agents are concerned that a wild monkey could carry rabies or even simian encephalitis.
"Apparently it's quite wild," the AQIS spokesman said.
"We will probably have to organize some kind of animal handler."
If the animal was caught it would sedated and euthanized, he said.
A spokeswoman for the RSPCA said she hoped the animal would be dealt with in a humane manner.