Schools should reopen before the six-week summer holidays if scientific evidence says it is safe to do so, headteachers have suggested.

But any return to normality will need to be planned, rather than "flicking a switch" before the weekend and assuming "it's all going to be all right on a Monday morning", the National Association of Head Teachers (NAHT) warned.

Schools in England closed three weeks ago due to the coronavirus outbreak, remaining open only for vulnerable youngsters and the children of key workers.

There is no indication yet as to when they may be able to reopen.

In an interview with Schools Week, NAHT general secretary Paul Whiteman suggested that schools should reopen as soon as it is safe to do so.

"We haven't seen any indication yet that the requirements of social distancing are such that things will change for schools in the short term," he said.

"That said, once the scientific advice is that schools can return safely, they should do so, even if it's for a very limited period before the summer break, as this will allow young people to reacquaint themselves with the educational environment.

"Any return to normality has to be a planned one. It can't be about flicking a switch on a Friday night and then thinking it's all going to be all right on a Monday morning."

Kevin Courtney, joint general secretary of the National Education Union (NEU), told the PA news agency: "When it is time for schools to reopen it will be very important for that to be planned with teachers and school leaders and for it to be phased.

"However, the National Education Union sees no evidence to justify speculation that this will be soon.

"We think such speculation is unhelpful because if people believe schools are reopening soon then they will be more likely to avoid other restrictions. It's vital that we stay indoors as much as possible to depress the spread of the virus."

Earlier this week, a study led by researchers at University College London indicated that school closures do not appear to have a significant effect on the spread of infections during outbreaks such as Covid-19.

Researchers found that school closures alone were predicted to reduce deaths by around 2% to 4% amid the Covid-19 outbreak in the UK, which is less than other social distancing measures.

A spokesman for the Department for Education said said: "Schools will remain closed until further notice, except for children of critical workers and the children who are most vulnerable.

"We will reopen schools when the scientific advice indicates it is safe to do so."