Children could be put in danger if the government goes ahead with plans to increase class sizes in the wake of a widespread outbreak of coronavirus in the UK, teachers and nursery workers have warned.

Rules around staff-to-pupil ratios in education and childcare settings could be relaxed as part of the government’s “battle plan” to combat the virus and ensure schools can stay open.

Teachers and children could be allowed to swap to different schools, and class sizes could be allowed to expand above the statutory limit under emergency measures.

But the National Education Union (NEU), the largest teaching union in the country, has warned that “cramped” classrooms will not keep pupils safe, adding that they could “do more harm”.

And the Early Years Alliance, which represents nursery staff, has said plans to relax staff-to-pupil ratios could have a “detrimental impact” on workers’ ability to protect children’s safety.

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The warnings come after the government set out its plans to rush legislation through parliament this month to give them extra powers to tackle the outbreak.

It is understood this will give schools and councils powers to suspend laws, including health and safety measures, to cope with a pandemic.

Kevin Courtney, joint general secretary of the NEU, said the union is planning to raise its concerns with the Department for Education (DfE) to ensure “no undue damage is done” to schools.

He said: “Schools have an important role to play, but we are concerned about suggestions in recent days that larger class sizes will be recommended for indefinite periods.

“These will benefit no one – a cramped classroom will not keep pupils safe, potentially doing more harm than good and arguably work directly against the ‘social distancing’ recommended in the action plan.”

He added: “Teachers will be angered at the prospect of an already strained service, with fewer teaching assistants in most schools, having to stretch further.”

Infant class sizes, for children aged between four and seven, are capped at 30 pupils per teacher.

But for younger children in early years settings the ratios are even lower. For under 2s, one adult is expected for every three children. For two-year-olds, it increases to every four children.

On plans to relax rules around staff-to-pupil ratios in childcare settings, Neil Leitch, chief executive of the Early Years Alliance (EYA), warned that workers would have less time to look after each individual child.

He told The Independent: “Even the very best practitioner only has one pair of hands and one pair of eyes, and so any change to current rules has the potential to have a detrimental impact on the quality of care that providers are able to provide, and their ability to protect children’s safety and wellbeing.”

“We hope any decisions made will be considered and well thought out, and not simply a knee-jerk reaction that ignores the specific care needs and requirements of very young children,” he added.

Matt Hancock, the health secretary, confirmed on Tuesday that 10 schools had closed nationwide, but he said schools should not be closing unless there is both a positive case of coronavirus and the school has had advice to shut from Public Health England (PHE).

A 1,000-pupil academy became the latest school to close its doors over the coronavirus crisis despite official government advice stating students should not be routinely sent home.

Hilbre High School on the Wirral sent its students home after head Mark Bellamy decided to close down the school “as a precaution” after a parent with pupils at the school tested positive for coronavirus.

Other schools have asked pupils to self-isolate, with many schools having pupils return after the half-term break from school skiing trips to northern Italy.

The Department for Education (DfE) has launched a new helpline to manage increasing queries about coronavirus and schools.

Announcing the government’s emergency plans on Tuesday, Boris Johnson said: “It is necessary to have some legislation in respect of things like school operations, borders, quarantine but these are exceptional and short term. They are not intended to last beyond the outbreak.”

A government spokesperson said: “Our action plan sets out measures to respond to the Covid-19 outbreak that are reasonable, proportionate and based on the latest scientific evidence.