Philippine officials are scrambling to head off a public health crisis as they try to contain the spread of the coronavirus through the country's notoriously overcrowded prisons.

Nine inmates and nine staff members at a city jail in the capital Manila have tested positive for Covid-19, the disease caused by the virus.

The prison authorities have taken 40 inmates to an isolation facility in the outskirts of metropolitan Manila, and were set to conduct targeted testing at the Quezon City Jail, north of Manila, where the outbreak was detected.

An inmate there died on March 25. While the autopsy report said it was due to hypertension and a heart condition, it noted "possible Covid-19" as a factor.

The report prompted prison officials to do contact tracing in the crowded facility, which has a capacity of only 800 but houses more than 3,800 inmates.

Jail chief inspector Xavier Solda, a spokesman for the Bureau of Jail Management and Penology (BJMP), told reporters in a video-conference on Friday that Philippine prisons have been in lockdown since early last month, when visits were disallowed.

A paralegal staff member at the Quezon City Jail tested positive for Covid-19 last month, but Mr Solda said she did not have contact with the inmate who died.

The staff member is now recovering at home. The other nine jail staff are also on home quarantine, having only mild symptoms such as cough and a sore throat.

Mr Solda said they are following health department protocols and disinfecting the prison regularly.

As of yesterday, the Philippines had reported 6,259 confirmed cases and 409 fatalities from the virus.

Local Government Undersecretary Jonathan Malaya has called on local government officials who are conducting testing for Covid-19, particularly those in Metro Manila, to include in the testing inmates in their city jails who are showing symptoms linked to Covid-19.

Mr Solda said the nine inmates and nine jail staff who tested positive were among 78 people tested for Covid-19.

A congressional committee recommended earlier this month the creation of an ad hoc committee that would evaluate the situation in Philippine jails and set up guidelines and procedures "for the temporary release by Philippine courts of qualified PDLs (persons deprived of liberty) for humanitarian reasons, in view of the national health emergency caused by the Covid-19 pandemic".

It also recommended prompt Covid-19 testing for inmates who display symptoms, prior to their temporary release.

The BJMP has supported the recommendations, noting that "jail decongestion at this point in time is an immediate and effective response to combat the Covid-19 pandemic".

The Department of Social Welfare and Development also supported the move, while the Justice Department said it had pushed for the release of the elderly and the sick even before the pandemic broke out.

Last Friday, the Supreme Court requested the Solicitor-General to comment on a petition filed by 22 political prisoners, asking for their temporary release and the setting up of a mechanism for the release of prisoners in a similar situation.

There are close to 134,000 inmates in the Philippines. Mr Solda said the national congestion rate is currently at 534 per cent.