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When I was inside the crater of Mt. Vesuvius in Naples, I was less alarmed by the smoking fumeroles that were expelling clouds of gas around her, than the ground giving away beneath me.

I was there with a scientist from Naples University, Professor Benedetto de Vivo. He was so intent on pointing out the intricacies of the inside of the crater that he wasn't looking at the ground beneath him.

There was an enormous drop in front of us and the ground wasn't that stable. He told me there's a lake of magma about 12 kilometers beneath us, but at that point my main concern was falling rather than the thought of a massive eruption.

Cameraman Louie Eroglu and I filmed the mountain from all sides, including the towns in the so-called red zone that are at risk.

They say a volcano is only dangerous if there are people around it. In this case there are three million people and the major problem is that it so congested that if there is an eruption with little warning, it will be impossible for people to escape.

Unfortunately, there is a major disagreement among scientists, with some saying there will be several weeks' warning while others say it could be as little as a day. In spite of this, the authorities have allowed lots of high-rise buildings and have now given permission to build the biggest hospital in southern Italy, right in the path of the last lava flow from Vesuvius.

We've looked at what might happen if there is an eruption with a pyroclastic flow like the one that killed everyone in the Roman town of Pompeii in 79 AD. It's a terrifying proposition.

From Anne Maria Nicholson, Reporter