Refugee lawyers say the federal government's plans for Indian officials to interview 157 asylum seekers when they arrive on the Australian mainland is unprecedented and potentially illegal under refugee law.

Immigration Minister Scott Morrison said on Friday that the group of mostly Tamil asylum seekers, who have been held on a Customs vessel on the high seas for almost a month, will be moved to the Australian mainland.

The asylum seekers will be taken to Cocos Island on Saturday then flown to the Curtin Detention Centre in remote Western Australia.

Mr Morrison said the group will undergo identity checks from Indian consular officials and that none will be resettled in Australia. India has agreed to take back any of its citizens and will consider taking Sri Lankan nationals who are Indian non-citizen residents.

Sources said most of the asylum seekers are Sri Lankan nationals.