Bomb threats were received by a few schools in Delhi on Tuesday, making it the second such incident this week and the fifth in nine days in the national capital, officials said.

On Monday, around 20 schools including DPS RK Puram had received threat emails.

According to an official from the Delhi Fire Service (DFS), a call regarding a bomb threat was received from Crescent Public School in Saraswati Vihar, northwest Delhi.

The official said that personnel from the fire department, local police, bomb detection team and dog squad conducted a search, but nothing suspicious was found so far.

Some more schools have also received similar threat emails and checks are ongoing, the official added.

However, schools in Delhi-NCR switched to hybrid mode for conducting classes on Tuesday, following the re-imposition of anti-pollution measures under Stage 4 of the Graded Response Action Plan (GRAP).

Under the revised GRAP schedule, classes for students in grades 6-9 and 11 in Delhi, Gurugram, Faridabad, Ghaziabad and Gautam Buddh Nagar must operate in hybrid mode (physical and online) under Stage 4 but students in classes 10 and 12 are required to attend school in person.

On December 14, eight schools, including the same DPS RK Puram, had received a similar email, in which the sender threatened to carry out an explosion using "bomb vests."

Earlier, on December 13, about 30 schools received bomb threats via email, prompting a multi-agency search of their premises. At least 44 schools had received similar emails on December 9.

The Delhi Police Special Cell had registered an FIR in connection with the threat mail to 44 schools and initiated an investigation.