At least 40 schools received a bomb threat by email in Delhi on Monday demanding $30,000, ANI news agency said, while police officials conducted initial searches on school premises.

Schools, railway stations and airports this year have been subject to hundreds of bomb threats, which have later turned out to be hoaxes.

Airlines and airports in India received 999 hoax bomb threats from the start of the year until mid-November, and 12 people had been arrested during the same period, government data shows.

Two schools got the threatening email on Sunday night, which said multiple bombs were planted inside buildings and would be detonated if the sender was not paid $30,000, according to ANI.

Many other schools received the emails on Monday morning, prompting school authorities to call parents to take the students home for the day.

Parents were seen picking their children up from the gates of some schools as police checked school premises for suspicious items.

Police officials in Delhi did not immediately respond to a request for comment from Reuters.

In May, more than 50 schools in Delhi and the adjoining suburb of Noida received similar bomb threat emails that turned out to be hoaxes.