The immigration department is strongly denying allegations of slavery on board a vessel that docked in Bluff.

The "Southern Ocean" arrived last Friday with a dead Chinese national on board, along with 41 other people.

It left on Tuesday without three Vietnamese crewmen, who were later found on the outskirts of Invercargill.

The trio have been interviewed and Immigration New Zealand assistant general manager Peter Devoy says they did not discuss slavery or exploitation on the boat.

Two of the men are likely to be deported tomorrow, with the third given a two-week visa to seek medical treatment.

Glenn Simmons: Dead crewman a symptom of slave ships