A major fire on Thursday broke out at 'Mantralaya', the Maharashtra state secretariat complex that houses offices of the Chief Minister, key ministers and top officials.

Close to two hours after it was first noticed near the cabin of Tribal Welfare Minister Babanrao Pachpute on the fourth floor, the fire continued to rage till late in the afternoon even as fire fighters battled the leaping flames.

There was no immediate report of any casualty but several people were suspected trapped on the upper floors and terrace, prompting authorities to press into service contingents of the elite commandos of Force One and city police's Quick Response Teams. Two teams from the naval dockyard were also rushed.

Panic gripped the sprawling building, the seat of state administration, after the fire, first noticed around 2.45 pm, spread swiftly to fifth, sixth and seventh floors.

Towering plumes of blinding smoke soon engulfed the building making it difficult for the fire brigade to evacuate the stranded.

According to sources, nearly 5,000 people vacated the building within 20 minutes of the fire breaking out.

Fire brigade personnel with huge hydraulic ladders were seen bringing down those trapped.

Choking in thick black smoke, several people were seen standing precariously on the parapet and balconies, waiting to be rescued. Many could be seen rappelling down the ropes and drain pipes in a desperate attempt to escape.

According to sources, the Urban Development Department, which is embroiled in a controversy over the Adarsh scam, and departments of Home, Revenue and Industries were the worst affected by the fire.

The offices of Chief Minister Prithviraj Chavan and his Deputy Ajit Pawar on the sixth floor were also damaged.

An eyewitnesses said some people were injured but no immediate official confirmation was available.

Pachpute said he heard a blast soon after the blaze started. Though his staff used fire extinguishers to put out the flames, it spread rapidly.

"I ran down and pulled out my cabinet colleague Jayant Patil from his third floor cabin," Pachpute said.

Animal Husbandry Minister Madhukar Chavan said he heard several blasts in the air-conditioners at he attempted to escape.

Pachpute said the fire brigade started its work around 3.05 pm, nearly 20 minutes after the blaze started.

Mumbai Police Commissioner Arup Patnaik, who arrived at the spot, said the rear portion of the building had suffered the maximum damage but did not confirm if anyone was injured.

Efforts to douse the flames were hampered by winds, he said.

To persistent questions if Adarsh files had been destroyed in the fire, he said, "Our primary concern is to sort out the situation, to rescue people."

Chief Minister Chavan and Deputy CM Ajit Pawar were superivising efforts to quell the fire and rescue the trapped.