The building also houses the Federation of Indian Chambers of Commerce and Industry
(FICCI), said Rajesh Panwar, Delhi's deputy fire chief.
The fire started around 2 a.m. Tuesday (4.30 p.m. Monday ET), officials said. The museum, which was opened in 1978 by Indira Gandhi, has been renting the space from the FICCI.
India's Minister of Environment, Forests, and Climate Change Prakash Javadekar visited the site of the blaze Tuesday morning.
"This is tragic, the Natural History Museum is a national treasure... the loss cannot be counted in rupees," he said, according to the Times of India.
A ministry official said Javadekar asked for an assessment of the damage, including what artifacts were lost. "Once we have that in hand we will then look into how to restore any damaged artifacts."
Javadekar has also ordered an energy and fire audit of all the establishments that fall under the ministry.
The museum is the first and only natural history museum in India, said Vikas Rana, the museum's educational assistant. In addition to the flora and fauna collections, it also displays several fossils, one of which is the femur bone of a dinosaur belonging to the Sauropod group.
Staff were prevented from entering the building Tuesday.
"I'm very sad because we lost our office and we lost all the objects that we have there," said Rana, who has worked in the museum for 12 years.
Museum also houses reference library
The facility is also home to a reference library for scholars and has more than 15,000 books. One of the librarians said he was concerned about the state of the collection.
More than 110 firefighters were sent to fight the blaze and six of them were injured during the operation. They were hospitalized and are in stable condition.
Panwar said the fire was under control by early afternoon Tuesday.
No one was inside the building when the fire started, according to the FICCI, and the cause is being investigated. The FICCI offices and auditorium were unaffected, the organization said.