Parents in Surrey will be warned that schools may have to operate a four-day week next term because nearly 600 teacher vacancies remain unfilled.
The severe shortage has forced education director Paul Gray to draft a letter saying that headteachers and governors may have to take drastic action. Classes could be doubled up, the timetable cut and the length of the school week shortened.
The National Union of Teachers claims Surrey is one of many areas which could be forced to cut the school week in September.
General secretary Doug McAvoy said: "Mr Gray knows the depth of the crisis. We need a 35-hour weekly limit from the current review of teachers' workload, and we need an urgent and independent review of teachers' pay. This will make teaching more attractive and, over time, help solve the crisis."
However, figures released to shadow education secretary Theresa May show the Government is planning to cut its targets for recruitment to teacher training - by 800 places over the next three years.
Mrs May said: "Where does this leave their pledge to recruit 10,000 more teachers - or was that just another empty promise?" Current recruitment to teacher training is booming, with applications to graduate courses up more than a fifth, and a predicted doubling of those training "on the job" in schools.
The latest monthly data shows applications up more than 28 per cent for secondary postgraduate courses in England and Wales, and up 21.4 per cent for primary courses.
They are in line with previous months' data, which have shown big increases in applications compared to last year when recruitment was dire, and only saved from collapse by the introduction last March of pound;6,000 training bursaries.
Recruitment expert John Howson said the figures were good news. But while most primary teacher-training courses are now full, most secondary ones still have vacancies.
The Teacher Training Agency says more than 1,000 people have been offered places on the graduate teacher programme for this September.
More than 700 are training in shortage subjects, 510 in secondary and 202 in primary. And 44 places have gone to people currently working as teaching assistants.