(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.
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 can'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.