Backlogs at crematoria are building up in coronavirus hotspots, with some families facing a wait of several weeks before funerals can take place and pressure mounting on mortuary space.

With pressure on the funeral services sector set to increase over the next two weeks as the death toll from Covid-19 reaches a peak, dozens of emergency mortuaries across the UK are starting to take delivery of bodies for storage until cremations or burials can take place.

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A temporary morgue with capacity for 12,000 bodies at Birmingham airport is due to be operational by the end of this week, and another is to open at Southampton airport. A facility at a warehouse on the Hillington industrial estate in Glasgow will be in use by Monday, and a morgue on the site of the former RAF Cottishall near Norwich will be operational in the next few days. “Body handlers” started work at a temporary mortuary in east London this week.

The number of dead in London in the first week of April was up 160% on the average for previous years; in Birmingham, the number of deaths in the first two weeks of this month exceeded the total for April 2019.

Julie Dunk of the Institute of Cemetery and Crematorium Management said the situation was “already challenging” in some areas. “All crematoria are looking to see how they can increase capacity, with longer working days and services at weekends. People may have to wait up to four weeks [for a funeral], or use a crematorium in another area.”

Some cemeteries were considering digging graves in unused spaces, she said. “Hard decisions may have to be made.”

Eight out of 10 people who die in the UK are cremated, with 20% opting for burial. But some faith groups – notably Muslims and Jews – choose burial, creating additional pressure in areas where there are concentrations of those religions.

Gardens of Peace, which runs two private Muslim cemeteries on the edge of east London, posted a notice on its website on 1 April saying there was already a backlog of burials and warning that “we may also have to undertake multiple burials in a grave”.

A paper on pandemic planning, published last month by the University of Huddersfield, warned that death and bereavement services were likely to be overwhelmed. Based on research carried out last year, the paper listed among key challenges: delays in issuing death certificates; lack of equipment such as coffins, body bags and cremator ovens; a shortage of body storage space if funeral parlours, hospitals and mortuaries reach capacity; and a lack of cemetery space.

It said that, with a 2.5% mortality rate, “authorities will struggle to maintain death registrations and disposals that will potentially have serious consequences.

It suggested that “common burials or ‘mass graves’ … may become necessary during a crisis”, acknowledging “public acceptance could not be guaranteed” for such a move.

Last week, it emerged that a mass grave had been dug in New York, which was being used for the burial of people with no known next of kin or whose families could not afford a funeral.

Julia Meaton, one of the paper’s authors, said mass graves in the UK were unlikely if temporary mortuaries were used to slow the pace of funerals to a manageable rate. “I think as a nation we have enough capacity, but everything is devolved [to local authorities]. There is no national approach, no national strategy.”

The Deceased Management Advisory Group, an umbrella organisation for the death and bereavement services sector, is liaising with the government and local resilience forums, set up under the Civil Contingencies Act of 2004, which include emergency services, local authorities, the NHS, environment agency and others.

According to Deborah Smith of the National Association of Funeral Directors, some smaller funeral firms are on the point of reaching capacity, and all are “incredibly busy”. She said: “In some areas, there is a wait building up at crematoria, and some funeral directors are struggling with the supply of body bags.”

Terry Tennens, chief executive of the National Society of Allied and Independent Funeral Directors, said there were backlogs in “hotspot areas” such as Birmingham, which were creating “storage challenges”.

He added: “The capacity crunch is linked to crematoria’s ability to carry out a finite number of cremations in a day. Many are putting in place measures to increase the number of cremations each day but it’s safe to say that in harder-hit parts of the country the backlogs will continue for several more weeks.”

Additional pressure on mortuary space is coming from families seeking to delay funerals until restrictions on gatherings are relaxed.

Sharon Thompson, a Birmingham city councillor, said: “Some people want to hold back, and we are seeing strain in the system. We are now starting to need our temporary mortuary facilities.”

The council had extended crematoria operating hours and was preparing burial sites “at greater pace”, she said. It was working with funeral directors, community groups and faith organisations to encourage funerals to take place as soon as possible and to explain restrictions on attendance.

The next couple of weeks would be critical. “We are having to deal with this in real time. It’s a very pressurised set of circumstances.”