Environmentalists are warning of a repeat of the disaster which befell large parts of South East Asia two years ago unless action is taken to curb a string of forest fires in the region.

Watch David Willis' report from the Indonesian island of Sumatra

Haze from the fires has once again started to spread across the area prompting Indonesia to declare a state of emergency in one of its worst-affected areas.

A faint glimmer of hope spread through Pekanbaru this week - heavy rain, the first downpour for several weeks, set people wondering whether an end to their siege-like situation may finally be close at hand.

For two weeks some had virtually been prisoners in their own homes, unable to venture out because of the smog which hung like a blanket over this once bustling city.

Schools and kindergartens closed their doors after the local air pollution index, which usually peaks at 50, soared above 900.

A local hospital has reported more than 300 cases of haze-related illnesses, such as asthma and bronchitis in less than a fortnight, many of them affecting children younger than five.

Fires spreading

Satellite images show how rapidly the fires are spreading. At a European Union-funded research centre in southern Sumatra, scientists fear that unusual weather patterns, such as a prolonged drought induced by El Nino, could turn the current situation into an environmental catastrophe.

Some villagers are paid to start fires

Dr Roderick Bowers, head of the Forest Fire Prevention Project, said: "El Nino events are becoming more common. We cannot prophesy when the next one will be. If it comes too quickly and Indonesia is not fully prepared, we could be looking at a disaster."

Travelling into the rain forest, it swiftly became apparent the worst is yet to come.

Wealthy and well-connected plantation owners are being allowed to raze the forests in order to plant lucrative crops, such as palm oil, which is used to make margarine.

Firestarters rewarded

And while some local villagers are helping to fight the fires, others are being paid to start them.

I came across three young men, armed with kerosene and plastic cigarette lighters who admitted setting fire to the forests in return for less than three dollars a day.

"I know it's wrong," one of the men told me. "But I have no other means of earning money to support my wife and family."