Smog has become an annual problem in Malaysia, but this is the first time in eight years that a state of emergency has been called, the BBC's Jennifer Pak, in Kuala Lumpur, reports.
People are angry that the authorities have not been able to address the health hazard, our correspondent says.
The smog is being blamed on illegal land-clearing fires burning near the provincial capital Pekanbaru.
Palm-oil firms - some of which are based in Malaysia and Singapore - have been accused of using slash-and-burn techniques to clear space for their plantations.
Environmental group Greenpeace International said its analysis of Nasa data between 11 and 21 June had "revealed hundreds of fire hotspots in palm oil concessions".
Slash-and-burn clearances
- Vegetation is cut down and burned to clear land for cultivation
- Cheaper than using excavators and bulldozers
- Illegal burning of forests to clear land for palm oil plantations is common in Indonesia - particularly in dry season
- Indonesia says it is investigating several palm oil companies