Jakarta (ANTARA News) - Environmental group Greenpeace called Wednesday on Indonesia to halt land clearing fires, warning that thick haze from the blazes threatened the health of millions of people and contributed to climate change.

"Greenpeace is calling on the Indonesian government to stop all land clearing operations in fragile forest environments in order to break this annual cycle, which is destroying large tracts of forests in Sumatra," the organisation was quoted by AFP as saying in a press release.

Haze would continue to smother Southeast Asia annually if Indonesia failed to stop the burning of peat forests -- a type of forest which is widespread in Sumatra and Indonesian Borneo -- the group said.

"Once these peat swamps are exposed due to logging, clearing for canals and concessions, they dry out like a wet sponge exposed to sunlight and become extremely flammable," said Greenpeace campaigner Hapsoro in the statement.

"Unless the conversion of these types of forests is stopped we will continue to experience large scale forest fires and continued environmental destruction on an annual basis," he added.

Indonesia's neighbours have urged it to curb the annual haze crisis by cracking down on forest fires, warning that it is hurting business and putting off tourists.

Greenpeace blamed industrial forest concessions after carrying out an investigation in Sumatra.

"Forest clearing for acacia pulpwood and oil palm plantations are the leading causes of the fires and also a factor in creating environmental conditions that perpetuate the problem."

It alleged that conversion of peat land and forest fires was releasing massive quantities of carbon dioxide (CO2) into the atmosphere further adding to the problem of climate change.

Greenpeace also urged the government to declare the fires a national emergency and to prosecute plantation companies found responsible for the slash and burn land clearing.

Earlier Wednesday, thick haze stopped air traffic in and out of an airport in West Kalimantan province, a local meteorological agency said.

Police in Jakarta meanwhile said they were investigating companies suspected of starting fires. Although the government has outlawed clearing land by fire, enforcement has been weak.

The police statement came after the Jakarta-based environment group Walhi demanded the investigation of more than 100 palm oil and industrial forest companies for allegedly starting fires.