At least 30 people were injured after a car exploded in the centre of the southern Russian city of Pyatigorsk on Tuesday, a local emergencies department source said.

"Three of the wounded are in a critical condition," the source said.

An explosive device was detonated in a Lada car parked near a cafe at 16:15 Moscow time (12:15 GMT).

A criminal case has been launched on charges of terrorism, said a spokesman for the Russian investigations committee said.

President Dmitry Medvedev has ordered the Federal Security Service and the Prosecutor General’s Office to investigate the Pyatigorsk explosion, a Kremlin representative told Itar-Tass.

Federal Security Service Director Alexander Bortnikov “immediately informed the president about the Pyatigorsk explosion and measures taken in that connection,” he said.

“Dmitry Medvedev ordered Health and Social Development Minister Tatiana Golikova and Stavropol Governor Valery Gayevsky to assist the victims,” the Kremlin said.

Detectives of the North Caucasus and South Federal Districts Department of the Investigation Committee and forensic experts are working on the crime scene. Deputy Presidential Representative to the North Caucasian Federal District Vladimir Shvetsov is also there.

The Pyatigorsk administration formed the operative staff and opened a hotline for providing information about explosion victims.

Pyatigorsk is the capital of Russia's North Caucasus Federal District, which includes the volatile republics of Chechnya, Dagestan and Ingushetia, where terrorist attacks and militant clashes are common.