The forest fires blanketing Malaysia, Singapore and large parts of Indonesia in choking haze are on track to become among the worst on record, NASA warns.

The region has suffered for years from annual bouts of smog caused by slash-and-burn farming on the Indonesian islands of Sumatra and Kalimantan.

An El Nino weather system has made conditions drier than usual in Indonesia, but authorities are hoping much-needed rains will arrive within a month to douse the blazes.

Scientists predict the current outbreak could surpass 1997 levels when out-of-control forest fires sent pollution soaring to record highs in an environmental disaster that cost an estimated $US9 billion.

If the forecasted dry conditions extend, the region could be enveloped in an even denser smog.

"Conditions in Singapore and south-eastern Sumatra are tracking close to 1997," said Robert Field, a Columbia University scientist based at NASA's Goddard Institute for Space Studies.

"If the forecasts for a longer dry season hold, this suggests 2015 will rank among the most severe events on record."

Fire alert count across Sumatra January 1, 2013 to October 2, 2015 ( fires.globalforestwatch.org )

This year's smog crisis has seen flights grounded, schools closed and tens of thousands of people seek medical treatment for respiratory problems.

Indonesia is receiving heated criticism from neighbours for not doing enough to address the problem, even as its environment ministry said it is taking legal action against four companies and is investigating about 200 more.

Jakarta has also deployed more than 20,000 personnel to fight the fires through waterbombing and chemically-induced rainfall.

The NASA-linked Global Fire Emissions Database has estimated around 600 million tonnes of greenhouse gases have been released as a result of this year's fires, roughly equivalent to Germany's entire annual output.

World Cup swimming meet threatened

FINA, swimming's world governing body, is considering cancelling this weekend's World Cup swimming meet in Singapore if the air quality worsens further.

Officials have already cancelled the 800 metres and 1500m events because of concerns for the health of competitors.

The fate of the meet, which is the fifth leg of the annual global World Cup series, would depend on Pollutant Standards Index (PSI) readings, FINA executive director Cornel Marculescu said.

The PSI levels, determined by Singapore's National Environment Agency, have consistently been over 100 in the past few weeks, putting them in the "unhealthy" range.

"In the event that the 3-hour PSI reading exceeds 200, and enters the very unhealthy range, no races will take place," Mr Marculescu told a news conference.

Mr Marculescu said FINA held talks with the swimmers on Friday to brief them about the situation and explain the various contingency plans in place.

"We are deeply disappointed with the haze threat," he said.

"However, the health and safety of our athletes, guests, officials, volunteers, spectators and staff are our top priority."

Air pollution levels have climbed to "very unhealthy" levels in Singapore, according to the National Environment Agency. ( AFP: Roslan Rahman )