The private Dogan news agency said police had to use tear gas to disperse an angry crowd that gathered at the scene of the blast in the city of Hakkari.
No one immediately claimed responsibility for the explosion, but Kurdish rebels who are fighting for autonomy in the region have used roadside bombings against military and police vehicles there in the past.
Gov. Muammer Turker told Turkey´s state-run Anadolu Agency that the explosion occurred on a busy street in the southeastern city as the police vehicle was driving by.
The blast wounded a total of 28 people, including seven policemen, and one of the civilians died at the hospital, Turker said.
TRT, Turkey´s state-run television, said the explosion was caused by a roadside bomb targeting police. The pro-Kurdish news agency, Firat, said the explosion was caused by a bomb that formed a large crater on the ground and shattered the surrounding buildings´ windows.
Kurdish rebels, who belong to the Kurdistan Workers´ Party, have been branded as terrorists by the U.S. and the European Union. Tens of thousands of people have died during their battle for independence since 1984.