The government is considering releasing some offenders from prisons in England and Wales to ease pressures caused by the coronavirus pandemic.
Justice Secretary Robert Buckland said the virus poses an "acute" risk in prisons, many of which are overcrowded.
Some 3,500 prison staff - about 10% of the workforce - were off work on Tuesday because they were ill or self-isolating, a committee of MPs was told.
Mr Buckland said releasing some inmates could help to "alleviate" pressures.
The justice secretary told the Commons justice committee he was "keen" to make use of release on temporary licence - where prisoners are let out for short periods, after a risk assessment.
Mr Buckland said he was looking "very carefully" at whether or not 50 pregnant prisoners could be released.
He also indicated some of the 9,000 inmates who are on remand, awaiting trial, could be transferred to bail hostels, if it was safe to do so.
Mr Buckland said the prison service must "balance the protection of life with the need to protect the public", but releasing prisoners early could help to "alleviate some of the pressures" the virus was having on the system.
However, he pointed out that releasing more prisoners would be a "challenge" for probation staff.
Amnesty International UK's head of policy and government affairs, Allan Hogarth, said elderly prisoners and those with underlying medical conditions should "immediately" be considered for release "if they do not pose a threat to themselves or society".
Mr Buckland's appearance before the committee came as all visits to prisons were cancelled, as part of measures to curb the spread of the virus.
Outside visitors, group activities and education classes have all been banned and inmates have been confined to their cells for 23 hours a day.
The Ministry of Justice (MoJ) said 55 prisons across England and Wales would be given 900 phones to allow prisoners to stay in touch with family members during the ban.
The phones will not have internet access and would only be handed out to risk-assessed prisoners on a temporary basis, the MoJ said.
The justice committee also heard from Jo Farrar, chief executive of the Prison and Probation Service, who said 13 inmates had tested positive for coronavirus.
The confirmed cases were in nine prisons although more jails are suspected to have had cases.
According to the latest Department of Health figures, there are now more than 8,000 confirmed cases of coronavirus in the UK - although the actual number cases is likely to be far higher. Some 422 of those patients have died.
Mr Buckland said more tests for the virus were needed in prisons, and more personal protective equipment (PPE) was needed for staff.
About 50,000 protective masks have been delivered for staff to use and a ban on bringing hand sanitiser into prisons has been lifted.