Malaysia's premier has urged Indonesia to act against those to blame for raging fires that have blanketed Southeast Asia in smog for weeks, as Malaysian schools closed again Monday over health concerns.

The regional environmental crisis has caused flights and major events to be cancelled, and forced tens of thousands of people in Indonesia, Malaysia and Singapore to seek treatment for respiratory problems.

"They (plantation companies) are operating there, we want Indonesia to take action," Malaysian Prime Minister Najib Razak was quoted as saying by state news agency Bernama late on Sunday.

"Only Indonesia alone can gather evidence and convict the companies concerned."

The blazes flare annually during the dry season as fires are illegally set to clear land for cultivation on Indonesia's island of Sumatra and in the Indonesian portion of Borneo island.

Singapore consumer and environmental groups called Monday for a commercial boycott of "irresponsible" companies contributing to regional air pollution through the fires.

The non-government Singapore Environment Council and the Consumers Association of Singapore (CASE) issued an approved list of 10 paper-making companies.

The 10 have declared that they do not buy or use any materials from Indonesian producers which are facing legal action by Singapore.

Five firms operating on Sumatra, including global giant Asia Pulp and Paper, have received legal notices from Singapore which could result in huge fines.

They were the first companies openly named by Singapore as potential culprits under a newly activated law allowing the island republic to sue overseas firms found to have contributed to serious haze outbreaks.

Air quality was again in the officially "unhealthy" range in Singapore on Monday after a brief respite over the weekend.

CASE urged Singaporeans to "send a strong signal to the errant companies that consumers' goodwill should not be taken for granted and consumers will not support companies which are environmentally responsible and/or have contributed to the environmental disaster year after year".

Experts have warned that this year's flare-up is on track to equal or surpass an infamous 1997 haze outbreak that sent pollution soaring to record highs and caused an estimated $9 billion in economic damage across the region.

Indonesia has sent more than 20,000 troops, police and other personnel to fight fires in an effort that has included waterbombing and chemically induced rainfall.

Indonesian President Joko Widodo's office said he was "very serious in tackling the forest fires" but dry weather caused by the El Nino climate phenomenon posed a challenge.  

Presidential spokesman Ari Dwipayana told AFP that companies found to be responsible for lighting fires could have their business permits revoked, but added: "All this takes time."

Malaysian authorities ordered school closures last month due to bad air quality, and over the weekend announced schools across much of the country would close again on Monday and Tuesday.

Bernama said Najib, speaking on a trip to Italy, added that the haze was also affecting Malaysia's economy.

Indonesia has for years faced pressure from its neighbours to act but the haze recurs annually to varying degrees.

Singapore officials last week expressed impatience with Indonesia, and Malaysia's Najib said the three countries must work together to formulate an effective strategy to tackle the annual environmental disaster.

Poor air quality forced the cancellation of major events at the weekend.

In Singapore races in the FINA World Championship -- swimming's World Cup -- were called off on Saturday, and one of Malaysia's biggest marathons set for Sunday in Kuala Lumpur was cancelled.

Some local Malaysian football league matches have also been shelved.