The haze over Singapore has disrupted flights, with 12 private jets being turned away owing to poor visibility at Seletar Airport from last Saturday to 6pm yesterday.

Nine of the flights were redirected to Changi and the other three to Johor's Senai Airport, said Changi Airport Group (CAG) and the Civil Aviation Authority of Singapore.

So far, there has been no impact on operations at Changi, CAG spokesman Ivan Tan told The Straits Times.

Unlike the main airport, which has the equipment and technology to guide pilots even when visibility is poor, Seletar operates under visual meteorological conditions. This means pilots must be able to see the runway clearly before they are allowed to land.

If the haze worsens, the airport will have to shut down. The last time this happened was in June 2013, when visibility fluctuated between 700m and 1,200m, which was below Seletar's minimum operating requirement of 1,500m. At Changi Airport, the threshold is 350m.

Former pilot and current head of the diploma in aviation management programme at Republic Polytechnic, Mr H.R. Mohandas, said that with advancement in technology, it is technically possible for pilots to land "blind" with the use of auto pilot.

However, this is allowed, under international safety guidelines, only when certain criteria are met. These include airports and planes being equipped with the necessary capabilities, and pilots being trained to operate the flights. It is understood that Changi, like many other airports in Asia, is not authorised to execute such landings.

Mr Mohandas said: "This normally occurs in other parts of the world, for example in Europe and the United States, that are more prone to severe weather conditions like harsh winters and blizzards."

With the recent upward trend in Pollutant Standards Index (PSI) readings, the aviation authorities and airlines said they are monitoring the situation closely and will adjust their operations accordingly.

In the meantime, the airport has been working with its partners and agencies to take precautionary measures for the well-being of airport staff and to ensure they are adequately protected, Mr Tan said.

For example, notices and health advisories are displayed to inform airport staff working outdoors of PSI levels, and masks are provided.

Drivers in the airfields are also reminded to switch on their headlights during the day and to exercise extra caution, he said.