Malaysia on Thursday stepped up pressure on Indonesia to do more to stop outbreaks of smog after fires on Sumatra island sparked Southeast Asia's worst air pollution crisis for years.

Palls of smoke from slash-and-burn agricultural fires pushed haze levels to record highs in Singapore last week, shrouding the city in smog, and badly affected parts of Malaysia.

While smog is an annual occurrence during the dry season this year's outbreak has been the worst for years, sparking tension between Indonesia and its neighbours.

After meeting his Indonesian counterpart in Jakarta, Malaysian Environment Minister G. Palanivel urged Indonesia to ratify a key Southeast Asian treaty aimed at tackling smog.

"The environment minister has to deal with this ratification," he said.

"If they can ratify the treaty then they can go forward."

The Association of Southeast Asian Nations (ASEAN) agreement is aimed at tackling the annual outbreaks of smog by increasing regional cooperation.

It was struck in 2002 following Southeast Asia's worst haze crisis in 1997-1998, that was estimated to have cost the region $9 billion.

But while the ASEAN deal is principally aimed at stopping haze that comes from forest and slash-and-burn fires in Indonesia, Jakarta is the only member of the 10-country bloc yet to ratify it.

Environment Minister Balthasar Kambuaya said Thursday Indonesia was "in the process" of ratifying the treaty.

Palanivel said that a meeting between five ASEAN members on haze scheduled for August would be brought forward to July 17 due to the current crisis.

Highlighting raised tensions between Singapore and Indonesia, unidentified hackers on Thursday attacked the site of Singapore-based Eu Yan Sang, a leading retailer of traditional Chinese medicine.

"Do not blame Indonesia just because the air in your country is polluted," said a message posted by the hackers.

Thousands are tackling the fires, which are centred in Riau province on the island of Sumatra. The blazes eased Wednesday after heavy rainfall.

The skies in Singapore are now clear thanks to rains and favourable winds and in Malaysia on Thursday the haze eased dramatically as rain fell in many places after hitting hazardous levels in recent days.