Singapore continues to grapple with severe haze as smoke from wildfires in neighboring Indonesia drifts into the city-state, with Prime Minister Lawrence Wong warning of action against companies responsible for the fires.

Air quality in Singapore remained unhealthy on Thursday, as smoke from widespread fires in Indonesia’s Kalimantan region continued to drift toward the city-state, according to the National Environment Agency.

Singapore’s air quality first deteriorated to unhealthy levels on Sept. 4, the first time in nearly three years, according to government data. The worsening haze has cast a shadow over the city-state, disrupting daily life and threatening businesses as air pollution continues to worsen.

In a post on X Thursday night, Wong said the government was looking into companies potentially responsible for the forest and peatland fires in Indonesia. He said authorities could take legal action under Singapore’s Transboundary Haze Pollution Act where warranted, while also exploring joint action with other countries.

Singapore’s Seletar Airport has seen 16 diversions due to low visibility, spokespeople for Changi Airport Group and the Civil Aviation Authority of Singapore told CNBC in a joint media reply.

The prolonged haze is taking a toll on daily life and businesses, with some outdoor dining establishments, including outdoor dining restaurants and hawker centers, reporting a drop in business, according to the local media.

A spokesperson from Marina Bay Sands told CNBC via email that “certain outdoor experiences that involve prolonged exposure to the outdoors have been temporarily suspended” and the hotel is providing masks and air purifiers to guests.

Singapore’s Minister for Digital Development and Information Josephine Teo told CNBC’s “Squawk Box Asia” on Thursday that the haze was “not the best way to welcome our international guests,” as the city-state hosts Singapore International Cyber Week. The event has drawn a record turnout of more than 15,000 visitors from over 100 countries.

Teo said the government had begun preparations weeks earlier to support residents, including distributing masks to those most in need. While it remains unclear when the haze will improve, she said Singapore has been in close contact with Indonesian officials to understand their needs and stands ready to provide assistance.

A spokesperson of ride-hailing and delivery platform Grab told CNBC via email that they have been distributing masks and have issued advisories to their platform workers as well.

The haze has extended beyond Singapore, affecting neighboring Malaysia as well.

Malaysia’s Second Finance Minister Amir Hamzah Azizan told CNBC on Wednesday that the worsening haze requires a coordinated response across Southeast Asia, saying the country has offered to deploy water bombers and other resources to help tackle the issue. “It is an issue that needs an ASEAN solution,” he said.