SYDNEY (AFP) - Ten Chinese nationals were arrested in a suspected drug smuggling operation on a large commercial boat seized off Australia's southern coast, authorities said Friday (Dec 16).

The 50-metre vessel was spotted by an Australian Border Force aerial patrol and tracked as it moved down Australia's west coast, across the Great Australian Bight and towards the coastline of Tasmania, an island state south of the mainland.

Military personnel from a navy ship boarded the boat on December 12 and brought it to Tasmania's capital Hobart "on the basis of that vessel's suspected involvement in illicit drug smuggling", Australian Border Force Regional Commander James Watson told reporters.

"The behaviour of this vessel in its track and... loitering more than 200 nautical miles off the southern coast of Australia was really quite unusual, and that's what caused us to want to get on board and have a look at this vessel."

Watson said the alleged type and amount of drugs on board were still being determined, but added there was a "significant quality" of illegal substances and the "crew members are believed to be Chinese nationals".

"At this point, all I can say is that it's significant. There's a lot of resourcing which has gone into this because of the size of the vessel which is involved... it's going to take us a bit of time to go through that vessel in some detail." He could not say where the boat was registered.

Tasmania Police Assistant Commissioner Glenn Frame confirmed the 10 crew "would be taken into questioning" but that it was too early to say what charges they might face.