Lawyers fear the Turnbull government is secretly plotting the quick return of asylum seekers to Nauru after it allegedly suggested a 72-hour notice period for the deportations would soon be lifted, meaning they could be returned with little warning or legal help.

The Human Rights Law Centre said the government had indicated to its legal team that the notice period for many of the 267 asylum seekers and refugees "will soon cease to apply". The government undertook to provide the notice during a High Court legal challenge to offshore detention, which it won.

The centre's director of legal advocacy, Daniel Webb, said the government "appears to be moving to rapidly clear the way for fast-track deportations without notice".

"Not only does it want to be able to return 267 incredibly vulnerable people to harm, it wants to do so suddenly and secretively without warning," said Mr Webb.