Education secretary Michael Gove has called for longer school days and a cut in the length of holidays, which he said would improve performance and make life easier for working parents.

The reforms could allow state schools to choose to stay open until 4.30pm and introduce a shorter, four-week summer holiday for pupils from September next year, representing a profound change for parents used to tailoring their working hours to the classroom timetable.

Gove said the school system had been designed for a 19th-century agricultural economy and risked leaving British children trailing those in Asia. "It may be the case that there are one or two legislative and bureaucratic obstacles which prevent all schools moving in this direction, but I think it's consistent with the pressures of a modern society. I also think it's going to be family friendly," he said.

Christine Blower, general secretary of the National Union of Teachers, said Gove was "making policy up on the hoof," without regard for the evidence. "Teachers and pupils already spend longer hours in the classroom than most countries and also have some of the shortest summer holidays," she said.

"Independent schools in England and Wales, which often break for two weeks more during the summer and have longer holidays at other times of the year than their state counterparts, do not apparently feel the need to change and are apparently not suffering from their reduced hours."

The changes would require a rewriting of teachers' contracts, which Gove kickstarted this week by asking the independent School Teachers' Review Body to examine working hours. The current contract mandates that teachers work 195 days or 1,265 hours a year.

Gove told a conference in London, organised by the Spectator magazine, that pupils were being handicapped in comparison with their peers in other countries. "The structure of the school term and the school day was designed at a time when we had an agricultural economy," he said.

"I remember half-term in October when I was at school in Aberdeen was called the tattie holiday – the period when kids would go to the fields to pick potatoes. It was also at a time when the majority of mums stayed home. That world no longer exists and we can't afford to have an education system that was essentially set in the 19th century."

Gove gave the example of successful education systems in east Asia that demanded higher standards of their students and had longer school days and shorter holidays.

"We've noticed in Hong Kong and Singapore and other East Asian nations that expectations of mathematical knowledge or of scientific knowledge at every stage are more demanding than in this country," Gove said.

"In order to reach those levels of achievement a higher level of effort is expected on behalf of students, parents and teachers. School days are longer, school holidays are shorter. The expectation is that to succeed, hard work is at the heart of everything."

"If you look at the length of the school day in England, the length of the summer holiday … then we are fighting or actually running in this global race in a way that ensures that we start with a significant handicap."

Commenting on the speech, a Whitehall source said: "We can either start working as hard as the Chinese, or we'll all soon be working for the Chinese."

Under the current system, the school year is 190 days long. Pupils get around six weeks off in summer, two weeks at Christmas and Easter as well as three half-term breaks lasting a week each. School days usually run from around 9am to 3pm, or 3.30pm.

Some academies and free schools – which have more freedom to vary their operating hours – already keep their pupils in school for longer than state schools.

The Ark chain of academies, for example, has mandatory school hours of 8.30am-4.30pm on four days a week and holds remedial classes on Saturdays for pupils lagging in maths and English.

Other schools have varied the structure of the school year, such as the David Young Community Academy in Leeds, which has a seven-term year.

Asked if there was going to be a teachers' strike, Gove said: "Yes. There seems to be a competition between the NUT and NASUWT to compete for members, with each one trying to out-radical the other."

Gove made an offer to unions who complain about his reforms: "Many of [the teaching unions] have very passionate criticisms of the model of education that I've outlined and there's an open invitation to the unions which is: prove me wrong, set up a free school.

"If the NUT were to set up a free school, we would find them a building, we would fund it. And I would love to see an NUT or another union free school."

Turning down Gove's offer, a union spokesperson said: "The NUT is in a lot of places already. They're called schools."

At their Easter conference this year the NUT called for new limits on working hours amid concerns that school staff are facing "totally unsustainable" workloads.

Delegates backed a plan by the NUT's executive to draw up a draft contract setting out a 35-hour working week.

This would include 20 hours of "pupil contact time" - the equivalent to four hours a day in the classroom - as well as 10 hours for lesson planning, preparation and assessment, and five hours for "non-contact duties" such as staff meetings, parents' evenings and logging pupils' results.

Separately, universities minister David Willetts said he wanted to galvanise successful pupils from poorer backgrounds into applying to university – by sending them letters of encouragement from government ministers.