At least eight people were killed and 30 wounded in a suicide blast that ripped through a minibus in the southern Russian city of Vladikavkaz, officials said on Thursday.

The blast tore apart a bus packed with students in a busy main square in the centre of Vladikavkaz, a city in the North Ossetia region of the restive Russian Caucasus, witnesses said.

"According to preliminary information, the explosive device at the bus stop in the centre of Vladikavkaz was activated by a female suicide bomber," a statement by the regional administration said.

"Preliminary information suggests the explosion occurred most probably not inside the minibus but at the bus stop," a spokeswoman for the local branch of the interior ministry, Alla Akhpolova, told RIA Novosti news agency.

An AFP reporter saw fragments of human flesh scattered across the ground at the site, where large crowds gathered at a police cordon to glimpse the damage.

Amid conflicting reports, the head of the South Ossetia regional administration, president Teimuraz Mamsurov, said eight people had died.

The investigative committee of the Russian prosecution service pulled back from a claim 11 people had died and said the correct figure was eight, but an interior ministry official told RIA Novosti nine had died.

About 30 people were hospitalised with injuries: one of them was in a critical condition while five others were seriously wounded, a hospital official told AFP.

Russian President Dmitry Medvedev ordered investigators to carry out a "painstaking" probe, RIA Novosti news agency quoted the Kremlin press service as saying.

Initial reports had suggested the blast might have been caused by an exploding gas cannister, although officials at the scene later played down this explanation.

North Ossetia, which lies on Russia's southern border with Georgia, was the scene of the devastating 2004 school hostage crisis at Beslan. The region is also close to several regions racked by instability in recent years, including Chechnya, Dagestan and Ingushetia.

North Ossetian militias fought a brief war with forces from neighbouring Ingushetia in the early 1990s and tensions rose again after the Beslan attack.

Russian soldiers and police continue to be killed on a weekly basis by mainly Muslim insurgents, most notably in Dagestan, Ingushetia and Chechnya, the latter the scene of two full-scale wars since the 1991 Soviet collapse.