Rescue workers were searching for four people feared killed when fuel being loaded for a satellite launch rocket exploded and sparked a huge fire at India's main space centre on Monday.
A spokesman for the Sriharikota space centre in the southern Indian state of Andhra Pradesh, said that a medical team and fire-fighters were trying to enter the building, but falling debris was blocking them.
"The building is affected badly," spokesman C. Ravindranath said.
"There were seven people inside when the fire broke out. Three engineers managed to escape with severe injuries. The fate of four others who were inside is still not known," he added.
Ravindranath said that fire-fighters had been brought the blaze under control after battling it for two hours.
Site managers earlier said six people had been killed in the blaze, but senior officials were unable to confirm if there had been any fatalities.
An official at the site said the fire had triggered off an explosion that blew the roof of the building.
The chairman of Indian Space Research Organisation, Madhavan Nair, arrived in the southern Indian city of Madras late on Monday from Bangalore, to head for the site and supervise the rescue and clean-up operations.
Nair told reporters in Bangalore that the fire broke out as the propellant was being tested in the solid propellant space booster plant at the Satish Dhawan station.
"This seems to have happened while a propellant was being prepared for transportation. The propellant... caught fire and caused severe damage to the building in which the operations were going on," Nair said.
He added that the injured had been hospitalised with severe burns.
SK Das, ISRO spokesman, speaking in Bangalore said the station where the fire broke out had been cordoned off.
The space centre has a satellite launch pad, a technical center for rocket testing and assembly and a range of other facilities for launch control, satellite tracking and remote sensing.
The centre began operations in 1971 for the launch of rockets involved in India's domestic space programme.
The area surrounding Sriharikota is a high-security zone and kept under constant watch by Indian police.
Ravindranath said the accident would not hinder launches or other space programmes slated for the current year. "There will be no impact and all the programmes will go on as scheduled," he said.
He said that a new Geosynchronous Satellite Launch Vehicle, jointly being developed with Russia, and a Polar Satellite Launch Vehicle, would be launched from the site this year as scheduled.