SINGAPORE - Expect hazy conditions in Singapore to continue on Wednesday (Oct 7) as winds blow in haze from Sumatra.

The 24-hour Pollutant Standards Index (PSI) for the next 24 hours is likely to be in the mid to high sections of the unhealthy (101-200) range, the National Environment Agency (NEA) said in an update on Tuesday (Oct 6) evening.

The reading may drop gradually to the low end of that range if less dense haze is blown in, the agency added. Visibility is likely to remain poor, especially in the morning, but could improve throughout the day if the haze eases.

There may be some respite in the afternoon - thundery showers are in the forecast.

Air quality had deteriorated on Tuesday as Singapore residents woke up to haze-filled skies.

At 11pm, the 24-hour PSI was recorded at 133-167, in the mid to high-section of the unhealthy (101-200) band.

The three-hour PSI, which is not tied to a health-advisory, was 131.

The situation in Malaysia has worsened significantly. Air pollution in key areas such as Shah Alam breached the hazardous 300-point mark.

Malaysia's Education Ministry closed nearly 7,000 schools across the country for two days starting Monday, sparking concerns among parents as almost four million students were affected.

It has prompted Prime Minister Najib Razak to speak on the issue. Mr Najib, speaking to reporters on Sunday, urged the Indonesian government to take action against those responsible for the crisis.

On the home front, the Singapore Environment Council and Consumer Association of Singapore (Case) have released a list of companies which have declared that they do not use raw materials procured from the five Indonesian firms believed to be causing the ongoing forest fires.

There are currently 10 firms on the list, all of whom manufacture paper products sold in Singapore.

For local haze updates, go to the NEA website and the haze microsite, and follow NEA's Facebook page or Twitter account, or download the myEnv app.