The Fire department got a call regarding the blaze at 8:34 am. Twenty-five tenders were rushed to the spot, the officials said.
A CISF sub-inspector fell unconscious after inhaling the smoke and was taken to AIIMS, but he's safe now, they said, adding fire department personnel are trying to douse the flames.
Offices of the drinking water and sanitation ministry, forest ministry and a branch of the Indian Air Force are located in the Pandit Deendayal Antyodaya Bhawan, previously known as Paryavaran Bhawan.
The same building houses the National Company Law Appellate Tribunal (NCLAT), which is scheduled to take up Reliance Communications' insolvency plea today.