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.

1 dead as Typhoon Kalmaegi dumps heavy rains over central Philippines
Worker trapped under collapsed medieval tower in Rome dies, media says
Saudi Crown Prince bin Salman to visit Trump in White House
Man charged with 10 counts of attempted murder after knife attack on UK train
Tanzania's Hassan sworn into office after deadly election violence
Powerful 6.3 quake kills at least 20 in Afghanistan, hundreds injured
Turkey set to call for action on Gaza as soon as possible, source says
Hamas hands over three more hostage bodies
