'They keep firing shots from the bus from time to time,' a local police officer added. But the official Itar-Tass news agency said 16 of the hostages had been released.
It was the third seizure of a bus and its passengers in the region in the last six months. The hostage-takers were demanding dollars 5.8m (pounds 3.8m), a plane or helicopter, three assault rifles and three portable radios, the Itar-Tass news agency said.
They also wanted a second aircraft ready and waiting for them at Makhachkala, capital of Russia's Dagestan region on the Caspian Sea. Itar-Tass said the gunmen took over a local bus at mid-afternoon a few miles outside Mineralnyye Vody, a resort town about 1,300km (800 miles) south of Moscow.
The bus was travelling from Stavropol to Mozdok. The gunmen released six passengers to relay their demands to authorities, fired on a police patrol car, then drove the bus to the airport.
The report said negotiations were being carried out through one of the freed passengers, a woman whose child was still on the bus. A police duty officer in Mineralnyye Vody confirmed earlier that unidentified gunmen had taken hostages, but refused to give any other details.
The area around Mineralnyye Vody, which borders the Caucasus region, has become notorious for kidnapping in recent months. In December, four gunmen handed over a dozen schoolchildren for dollars 10m. In May, four gunmen traded a busload of hostages for a ransom said to be between dollars 4m and dollars 10m. The hostage-takers in both cases were captured and their captives freed unharmed.Reuse content