Air quality in Singapore deteriorated Thursday as haze continued to blow in from forest fires in the Indonesian island of Sumatra. Authorities said the hazy conditions could persist or even worsen later Thursday.

The 3-hour Pollutant Standards Index (PSI) increased to 219 at 10 a.m. local time (10 p.m. EDT), rising for a fourth hour, Bloomberg reported. A reading of between 201 and 300 is considered “very unhealthy.”

“Widespread haze is still persisting in southern and central Sumatra. For today, the prevailing winds are forecast to blow from the south-southeast or south-southwest,” the National Environment Agency (NEA) said Thursday, in a statement.

The agency advised people to avoid outdoor activities and physical exertion. People complaining of breathing problems should seek medical attention, NEA said.

“Given the air quality forecast for the next 24 hours, healthy persons should avoid prolonged or strenuous outdoor physical exertion. The elderly, pregnant women and children should minimize outdoor activity, while those with chronic lung or heart disease should avoid outdoor activity,” the agency added in the statement.

On Tuesday, over 150 Indonesians protested government inaction in managing the forest fires. The protests, in Central Kalimantan province, were led by students and volunteers of various Indonesian environmental groups. Demonstrators armed with placards also covered their faces with masks as the Pollution Standards Index level hit 1,400 Tuesday.