Smoke over swathes of Indonesia and Singapore was "tracking close to 1997" with forecasts pointing to a longer dry season, NASA's Robert Field said on Friday.
For weeks, residents in the region, including Malaysians, have sought treatment for respiratory problems, with Indonesia again facing pressure from its neighbors to tackle illegal burn-offs by plantation firms and small farmers.
The smog has disrupted aviation and forced school closures across the region.
Southeast Asia is currently in the grip of a so-called El Nino weather phenomenon, which makes conditions drier than usual.
Everything under control?
On Thursday, Indonesia's disaster chief, Willem Rampangilei, turned down a Singaporean offer to help by saying "everything was under control" and that he believed rains would arrive by early November.
More than 20,000 troops, police and other personnel were "working very hard" to douse fires burning in the regions of Sumatra and Kalimantan, he said.
His agency has also deployed 25 aircraft for water bombing and cloud seeding operations in the hope of triggering rainfalls.
Field, a NASA Goddard Institute for Space Studies scientist, together with other international researchers, published a series of research reports on the history of biomass burning in Indonesia since the 1960s.
Their reports published in 2009 said Indonesia was a "disproportionate contributor" via burning to atmospheric carbon dioxide, a key factor in clmate change.
Henry Purnomo, a haze expert at the Indonesia-based Center for International Forestry Research told the AFP news agency the magnitude of this year's fires was "horrendous."
"I believe the impact of the fires this year will be as bad as 1997, in terms of the cost," he said.
Last month, Indonesia's government declared an emergency for the island province of Riau.
The mayor of Pekanbaru, the province's capital, said he had prepared an air-conditioned hall to accommodate 100 families.
"The number of sick people is increasing and children are especially vulnerable to respiratory problems," said Mayor Firdaus, who goes by one name.
In all, Indonesia's disaster agency recently issued data showing that 177,000 people had suffered acute respiratory problems in seven provinces.
Indonesia's Environment Ministry has said it is taking legal action against four companies blamed for contributing to the smog.
ipj/sms (dpa, AFP, Reuters)