Sources said the two employees had been ''on constant'', meaning they were required to prevent asylum seekers on suicide watch from self-harming for the duration of their 12-hour shifts. ''It really does their heads in because they're watching people trying to kill or harm themselves all the time,'' one insider told Fairfax Media.

''The pressure of being with clients, at arm's length, for 12 hours a shift with no relief and seeing slashings and attempted hangings is taking a toll,'' said another.

Greens senator Sarah Hanson-Young, who was alerted to the situation by a Serco employee, said the plight of the guards represented ''a new chapter of misery'' in Australia's treatment of boat arrivals.

''These attempts by people to take their own lives on Christmas Island are not moral blackmail, as the Prime Minister has previously said. They are the result of the government's cruel and inhumane refugee policies,'' she said.

While a Serco spokesman would not comment on individual cases, he said precautions were taken where there were concerns.