Australia's search and rescue agency has been criticised in a classified government report as not being proactive enough in helping an asylum seeker boat that had made more than 16 calls for help over two days before eventually capsizing, killing 104 men.

The report into the incident, which has been kept under wraps since the tragedy unfolded in June last year, also revealed there was criticism of the Australian Maritime Safety Authority (AMSA) for handing over responsibility for the stricken boat to its Indonesian counterpart BASARNAS knowing that it had limited ability to conduct long-range search- and-rescue operations.

The report by Customs and Border and Protection was tendered in the West Australian Coroners Court on Wednesday during the resumption of an inquest into the sinking of that boat, which became known as the Kaniva or the SIEV 358 on June 21 last year.

It is believed there were 214 men on the boat - 210 were from Afghanistan, Pakistan, and Iran and four were Indonesian crew members.