NEW DELHI: Lakhs of children, many of whom had just finished a petrifying paper that capped the first board exam of their life and were about to set out on holiday trips, have been dealt the unkindest cut of them all: a mathematics retest on an unspecified date.

The Central Board of Secondary Education (CBSE) announced on Wednesday that it would re-conduct the Class X mathematics examination and the Class XII economics exam after both papers were leaked, affecting an estimated 20 lakh students across India.

The CBSE said the re-exam dates would be announced within a week. The government has said the difficulty level will remain unchanged.

This would be the first nationwide retest in recent memory. The scale could have been minimised had the CBSE retained its policy of drafting different question paper sets for different regions. The call for a nationwide retest has fuelled suspicion that the board had opted for a composite paper.

Officially, the Class XII exams will end on April 13 and the Class X exams on April 4. But for many Class X students, Wednesday's math paper was the last exam as the remaining subjects range from Sanskrit to painting.

Hours before the math exam was to begin on Wednesday morning, the questions were available on WhatsApp groups. Several parents in Delhi later complained that the questions circulated on social media were in the same sequence as they appeared on the question paper.

The questions asked in the Class XII economics exam, held on Monday, were available on WhatsApp before the test.

The CBSE, which falls under the administrative control of the HRD ministry, has taken up the issue with Delhi police.

"With the view to uphold the sanctity of the board examinations and in the interest of the fairness to the students, the board has decided to re-conduct the examinations in the following subjects," said a notice issued by the controller of exams, K.K. Choudhury.

Students, parents, schoolteachers and principals expressed anguish. "This is frustrating. I did very well in mathematics today. Now the exam will be re-conducted," said Ankita Prakash, a Class X student of Banyan Tree School in Delhi.

"The CBSE should declare the date for the retest at the earliest. In any case, our plans for vacations are now gone," she said.

Mala Gupta, a teacher at Springdale School in Delhi, said the leak and the decision to re-conduct the exams would disappoint students and parents, most of whom have planned their vacations in advance.

"The re-conduct of the tests will be on the back of their minds. They cannot go for vacations now," Gupta said.

A school principal said the re-exams should be held at the earliest so that the next academic session is not affected.

"This is shocking. The trust people have in the CBSE will be affected by these kinds of leak," the principal said.

HRD minister Prakash Javadekar, who addressed a news conference at the BJP headquarters on the violence in Bengal, was asked about the paper leak. He said some gangs were responsible for such offences.

"It seems a gang or some people are doing this deliberately. Delhi police have set up a special team and are investigating the matter. All these people will be caught. The police investigation is at an advanced stage," Javadekar said.

He said Prime Minister Narendra Modi had spoken to him on the paper leak.

Javadekar said safety preparedness had been revamped for the remaining papers. He said the difficulty level would be the same in the revised papers.

"I understand the misery of the parents and the students. But I want to assure them that the papers will not be leaked again," he said.

The CBSE had on March 15 received complaints of the Class XII accountancy paper being leaked. Delhi education minister Manish Sisodia had posted a tweet requesting the CBSE to take swift action. The CBSE had ruled out a leak.

There had been complaints of answer sheets of the Class XII chemistry paper being carried from the exam centre to the CBSE headquarters in a Delhi Metro train earlier this month.