Eight Chinese crew aboard a suspicious vessel seized off Western Australia's coast have been taken into immigration detention by the Australian Federal Police (AFP).

On Sunday, the foreign boat was intercepted off the coast near Geraldton, 400 kilometres north of Perth, and escorted to the Geraldton Fishermen's Wharf the following day.

The AFP confirmed the eight crew members on the boat had been detained as they "did not have valid visas to enter Australia".

The AFP did not say where the men were being detained but said no-one had been charged.

The joint investigation between the AFP, Western Australia Police and Australian Border Force is ongoing and the boat remains cordoned off.

A complete inspection of the vessel is expected to take a number of days.

Firefighters wearing hazmat suits and breathing apparatus removed several containers from the vessel, which is about 25 metres long, on Tuesday.

It is suspected the containers hold unidentified liquid chemicals.

The boat is being searched as investigations continue into how the vessel was being used.

Authorities have not confirmed whether the boat was disguised as a fishing boat and is linked to illicit drug activity.