By BBC News Online's Sanjoy Majumder in Delhi

At about 1130 (0600GMT), our morning editorial meeting at the BBC Delhi bureau was interrupted by the sound of loud explosions.

They appeared to have come from within the Indian parliamentary complex.

From our office, which overlooks the complex, we could see police and paramilitary troops running to take up positions.

This was followed by what were clearly the sounds of gunshots being fired.

Sirens blared as the roads approaching parliament were sealed - only police jeeps and ambulances were let through.

Confusion reigned outside as police prevented journalists and cameramen from entering parliament and kept them at a distance of at least 50 metres from the main gates.

Many people - including politicians and journalists - were still trapped inside and those outside walked around with a dazed look on their faces.

Casualties

Then the first of several wounded were brought out - a security guard quite obviously very seriously injured.

The prime minister called it an 'attack on the entire nation'

Soon after we could see elite commandos of the National Security Guard - called the Black Cats because of their ubiquitous black uniforms - jumping off their vehicles and rushing inside.

Most days they can be seen hanging out of ministers' escort cars as they whiz through Delhi's chaotic traffic.

Today they were being deployed for a far more dangerous task - to hunt down five militants suspected to have infiltrated the complex.

From inside parliament, journalists and politicians spoke on their mobile phones to those of us outside.

Many MPs and even some ministers were still inside, they said, but were safe.

Journalists had taken refuge inside ministers' offices. They spoke of chaotic scenes as the security forces exchanged fire with the militants even as wounded colleagues were carried out.

One television reporter said he saw armed men in white civilian clothes open fire inside one of the parliamentary gates.

It was clear that the men, whoever they were, had launched an audacious attack at the heart of India's democracy.