Border authorities deny 'prison ship'

Border protection authorities have denied they're running a "prison ship" off the coast of Christmas Island for asylum seekers arriving in Australian territorial waters.

Immigration officials faced a grilling, at a Senate estimates hearing on Monday night, about unconfirmed reports an asylum seeker boat was intercepted off Christmas Island in mid-May and its passengers are in custody on the Customs Ocean Protector ship.

Customs chief executive Michael Pezzullo maintained that only an illegal foreign fishing boat had been intercepted near Christmas Island recently.

Australian Greens senator Sarah Hanson-Young referred to reports Christmas Islanders saw clothing packs being taken out to the Ocean Protector.

But Mr Pezzullo refused to comment on logistics, operational matters or any legal advice about holding people in custody.

He rejected Labor senator Kim Carr's description that asylum seekers were being detained on a "prison ship".

"People are being held in secure circumstances and subject to operational orders," he said, adding they were appropriately cared for with adequate food and water.

Senator Carr asked how many people were in custody on the Ocean Protector and other vessels.

"I'm not going to discuss that," Mr Pezzullo said.

He would not confirm whether additional orange life boats had been purchased since $2.5 million was allocated last year.

Several life boats have washed up on Indonesian shores with asylum seekers on board.

The coalition government maintains there have been no successful people smuggling ventures since late December.

Officials refused to confirm reports nine asylum seeker boats had been turned back to Indonesia since late December.

In early May, Indonesian navy officers claimed Australian authorities added three people to an asylum seeker boat before sending it back to their country.

The Australian Federal Police are considering a request to investigate the matter, which legal experts say might constitute a people-smuggling offence under Australian law.

Operation Sovereign Borders commander Angus Campbell would not comment on the incident saying it was an on-water matter.