Australia’s immigration system and its detainees are under considerable strain, documents showed, with self-harm reports surging 12-fold as waiting times soar.

Compiled for a government committee examining Australia’s mandatory detention policy for asylum seekers arriving by boat, the official documents offered a rare and sobering insight into the troubled centres.

“Unfortunately, we have seen increased instances of unrest... as well as self-harm and sadly, on occasion, suicide,” Immigration Department chief Andrew Metcalfe told the committee.

There were 6,403 people in immigration detention as at June 30 this year, with the main facility on remote Christmas Island housing 759 – almost double its operational capacity.

The detainees were predominantly young men, more than half of whom came from Afghanistan or Iran, although the report showed the number of children rising to 964 in the past year.

The riot-hit Christmas Island centre has been overflowing since mid-2009, with its surging population accompanied by a spike in incident reports to 1,176 in the three months to June 30, from 83 a year earlier.

There were 104 disturbances in the period, nine classed as “major” and 35 people on protracted hunger strikes, with 83 self-harm attempts – 27 of them serious.

Sydney’s Villawood centre, also rocked by riots, suicides and protests, was in a similar state, with 451 incident reports in the three months to June 30 from 189 a year earlier, dominated by self-harm, unrest and aggression.