As of midday local time (0400 GMT) the Pollutant Standards Index (PSI) reading ranged from 60 to 72, according to the government agency for the environment.
A reading between 51 to 100 is in the moderate range.
The reading also carries a health advisory to reduce outdoor activities and prolonged exertion.
The smoky conditions blanketed the island from Thursday.
The haze was a result of “an increase in hotspot activities observed over Sumatra” in the past week, the agency said on its website.