SINGAPORE >> Singapore shut schools Friday and began distributing free anti-pollution masks to the elderly and other vulnerable people as a thick smoky haze cast covered the island-nation with pollution reaching its worst level this year.

The haze — a pall of grayness that resembles wintry fog and virtually obliterates the skyline while even seeping inside homes — is an annual problem for the region, resulting from forests being burned in neighboring Indonesia to clear the land for farming and plantations.

Repeated efforts to bring the offending companies to book have not helped. Meanwhile, people in Singapore, Malaysia and Indonesia suffer from the smoke, a serious health hazard, especially for the elderly, children and those with breathing problems.

The three-hour Pollutant Standards Index (PSI), which measures air pollution in the country, hit 341 on Friday morning, the highest level this year, before dipping below 300, the hazardous mark.

The government ordered all primary and secondary schools to be shut. Also, free face masks were being distributed at community centers across the island to the vulnerable from 10 a.m. to 10 p.m.. Volunteers were also expected to go house to house to give out the masks to those who were unable to come to community centers.

The haze is also causing tensions between Singapore and Indonesia, apparently after Indonesian Vice President Jusuf Kalla commented recently that neighboring countries "already enjoy 11 months of clean fresh air from Indonesia." He suggested that it is not a big deal if they suffer from the haze for one month, when forests are usually burned.

Singapore Foreign Minister K. Shanmugam, in a Facebook post, responded by saying his government "takes the matter seriously" and Singapore is "ready to assist Indonesia in combatting the fires."

"Yet, at the same time, we are hearing some shocking statements made, at senior levels, from Indonesia, with a complete disregard for our people, and their own — PSI levels in parts of Indonesia are at almost 2,000 PSI."

"How is it possible for senior people in government to issue such statements, without any regard for their people, or ours, and without any embarrassment, or sense of responsibility?" he wrote.

The haze has also hit hard festivities in Singapore whose multi-ethnic population celebrated the Muslim festival of Eid al-Adha on Thursday and will mark the Chinese mooncake festival on Sunday, traditionally held by farmers to celebrate their autumn harvest.

"The haze is very bad, there are less people in the mosque this year. Coming to the mosque to pray used to be very nice because we would mingle around after," said Mustafa Muhamad, 61, who had come to the Hajjah Fatimah mosque to pray.

On Tuesday, Indonesia’s environment and forestry ministry said the licenses of four Indonesian plantation companies were suspended or revoked for clearing land illegally and sparking forest fires.

Some 27 companies are being investigated in connection with the forest fires, Indonesian authorities said, while 140 individuals are being questioned. A Singapore-listed company is among those under investigation.