Staff and pupils at one in five schools have been infected with Covid-19 so far this term, according to a new snapshot survey.
Figures obtained by Tes show that there have been more than 1,000 schools in England with at least one positive coronavirus test result across 40 council areas since the beginning of last month.
The survey results cover council areas with a total of 5,723 state schools – more than a quarter of those across the country. It reveals that 1,172 (20.4 per cent) of these schools have been hit by Covid-19.
This resulted in the bubbles closing or partially closing in 590 cases and the complete closures of 18 schools.
The data also reveals that some areas of the North of England have seen major disruption, with significant numbers of schools being forced to send staff and pupils home because of outbreaks.
There are at least five areas in the region where half or more of state schools have had a positive case of Covid-19.
Coronavirus: Teachers miss lessons through lack of tests
And 16 councils in England reported that a quarter or more schools in their districts have staff or pupils who have tested positive for the virus.
In Oldham, in the North West, all 15 of the town's secondary schools and three-quarters of its primary schools (69) have had a positive case. This has resulted in 158 school staff and 3,220 pupils self-isolating.
In Birmingham, there were almost 13,000 pupils forced to self-isolate as a result of Covid cases in schools last week.
Snapshot figures provided by the city council showed that, as of 25 September, 112 schools had bubbles closed or partially closed out of 443 schools in the city.
All these cases have come in the first of month of the new school term.
The new figures follow official data published this week by the Department for Education (DfE) which showed that the proportion of "fully open" state secondary schools fell by 8 percentage points last week – from 92 per cent on 17 September to 84 per cent on 24 September.
"Of those not fully open, this was mostly due to Covid-19 related reasons," the DfE said.
Six areas had at least 50 per cent of schools with Covid cases. In Oldham, 78.5 per cent of schools had at least one case.
Bradford Council said that of the 214 schools in the district, 115 (53.7 per cent) had a positive Covid case. This resulted in a bubbles being shut down in 80 schools.
More than half of schools in South Tyneside (33 out of 62) had positive cases (53.2 per cent) and also in North Tyneside (41 schools out of 79 – 51.9 per cent).
In both Bury and Sandwell, the figure given was 50 per cent.
Mary Bousted, joint general secretary of the NEU teaching union, said: "These are concerning figures and especially because this is just the beginning. We know the cases are rising and that this is going to get worse.
"It is also concerning because of the amount of disruption this it is going to cause to schools and to pupils' education.
"The decision to stretch the idea of a bubble to breaking point by talking about whole year group bubbles at secondary school is coming to roost now because schools are having to take decision to send home whole year groups and this was always going to be the problem."
The NEU has called on the government to reduce the number of pupils who need to be sent home by creating smaller classes. It said the government needs to create extra learning spaces through "nightingale classes" to achieve this.
It has also launched a new website which will provide weekly updates on the level of coronavirus cases around each school in the country. People can also use the site to call for more testing in schools.