( CNN ) -- Singapore was shrouded in haze on Wednesday as smoke from forest fires in nearby Sumatra drifted across the Malacca Strait in the city 's worst pollution crisis in more than a decade . Buildings in the city of 5.3 million people have been enveloped in a smoky haze since the beginning of the week as illegal burn off in nearby Indonesia and prevailing winds were causing a smoke crisis not seen since 1997 . Interactive : See the smog descend on Singapore . Singapore 's pollution index reached 371 on Wednesday , the worst level since 1997 when it reached 226 , according to the Straits Times . The city 's National Environment Agency said air quality becomes 'very unhealthy ' when the index passes 200 . The agency said that thick haze would continue for the next few days as forest fires were still raging in Sumatra . Singapore 's Environment and Water Resources Minister Vivian Balakrishnan said he would urge commercial pressure against firms causing the haze . Critics have accused Singapore and Malaysian palm oil companies of investing in Indonesian companies that are clearing land for palm plantations . Dr Balakrishnan said on his Facebook site that he had approached his Indonesian counterpart , Balthasar Kambuaya , to express his `` deep distress '' at the situation . `` I suggested Minister Kambuaya name the companies responsible for the fires , '' Dr Balakrishnan posted on the site . Singapore residents , meanwhile , could be seen around the central business district wearing facemasks or handkerchiefs . `` I can say it 's actually getting worse , '' a Singapore-based energy industry analyst who did not want to be named told CNN . `` The staff are taking pictures out of the office window because you ca n't see the cruise ship terminal which is only 500 metres away . '' He said for three days the city has been under a pall of wood smoke that gave Singapore 's normally highly urban central business district the smell of a campfire . `` It gives off this smoky smell like you 've been sitting a bit too close to the hearth , '' he said . `` Whoever would have thought that I 'd be going to Hong Kong for a weekend simply to get a breath of fresh air . '' Authorities in Singapore are anxious to avoid a repeat of the 1997 Southeast Asian haze which the government estimates cost $ 9 billion in health care costs and disrupted air travel and business .
Singapore enveloped in a thick pall of wood smoke caused by forest fires in Sumatra . Pollution index reaches 226 on 1997 , the worst level since Wednesday when it reached 200 . National Environment Agency says air quality becomes 'very unhealthy ' when the index passes 200 . Singapore is anxious to avoid a repeat of the 1997 haze crisis which cost $ 9 billion .