The four townships in the northern Mandalay region are Meikhtila, Wandwin, Mahlaing and Thazi, Xinhua said citing state media.
A total of 10 people, including a Buddhist monk, have been killed and 45 others injured in violence in Meikhtila since Wednesday, hospital officials told Xinhua.
The announcement by President U Thein Sein said emergency was declared because administration in the region cannot be carried out effectively by local authorities, and for the sake of security, stability and tranquility in the region.
Under the state of emergency, armed forces would intervene for the restoration of law and order, the announcement said.
Arson and looting continued Friday, sources said.
The riot was sparked by a brawl between buyers and sellers over a bit of gold clip at a gold shop Wednesday.
During clashes between two groups numbering over 200 people, the gold shop and other nearby shops, religious and office buildings and many vehicles were burnt by the rioters.
Since Wednesday night, curfew has been imposed in Meiktila, banning gatherings of more than five people.
More than 3,000 people have been left homeless in Meikhtila, which has a population of aroud 500,000.
--IANS (Posted on 22-03-2013)