The Maritime & Port Authority of Singapore (MPA) has warned that haze could “significantly reduce” visibility in the Singapore Strait and port waters.

Smoke haze from land clearances in neighbouring Indonesia returned to the city state at the weekend, also affecting one of the world’s busiest shipping lanes and ports.

“Due to the presence of haze, the visibility in the Singapore Strait and port waters could be significantly reduced,” MPA said in a circular to the shipping community.

“During periods of restricted visibility, shipmasters are advised to keep a proper lookout and navigate with caution.”

As of 1500hrs on Thursday Singapore’s pollutant standards index (PSI), used to measure the haze, stood at 103, putting it in what the National Environment Agency (NEA) classifies as the unhealthy range. In a statement on Wednesday NEA noted: "Some of the haze has spread to the southern parts of the South China Sea".

The haze is a recurring problem and hit a high in June 2013 when the PSI crossed 400 mark which is considered hazardous.