Singapore said on Friday it was "ready to roll out" a haze pollution action plan that included the distribution of masks, as air quality dipped towards "very unhealthy" levels.

The city-state was regarded as the "most polluted global major city" early Friday, according to a Swiss-based air quality monitor, as toxic haze from fires in neighbouring Indonesia continued to drive up air pollution levels.

"Based on the current situation it is possible" that air quality levels "may enter the very unhealthy range," Singapore's National Environmental Agency said in a statement.

The NEA and other agencies "stand ready to roll out the next tier of action plans and advisories to protect the health and well-being of the public," it said.

It said the government has set aside haze-rated masks and if pollution levels dipped into very unhealthy levels, "grassroots organisations will start distributing N95 masks to eligible Singaporeans".

"To complement... distribution, mask vending machines will also be made available at selected public transport hubs and social services offices," the NEA added.