Najib made the declaration after the haze exceeded 500 on the Air Pollutants Index, Bernama, Malaysia's official news agency, reported.
As of Sunday morning the API was at 746; any reading above 300 is considered hazardous.
"This haze emergency declaration does not involve imposition of a curfew and also there is no change in the method of administration either at the state or federal level for now," the prime minister said.
The state of emergency will be in place until the haze dissipates, Bernama said.
When a Haze Disaster Emergency is declared, federal, state and district disaster management committees are required to take a number of actions, the news agency said.
Such actions include advising government and private sector work places on closing their facilities; close schools in the disaster area; and increase awareness of the state of emergency through television and radio.