The hospital was completely demolished and surrounding buildings gutted. Television footage showed diggers searching through the rubble around a deep crater.

Witnesses said an explosives-packed truck driven by one man had smashed through the hospital gates late on Friday, collapsing most of the four-storey building on top of itself.

The death toll was still uncertain, but news agencies said as many as 18 people were still under the ruins.

"At nine o'clock today, we had taken 33 corpses out of the ruins, and another two were on their way to being taken out," Nikholai Lityuk, deputy head of the Emergency Ministry's southern center, told NTV television.

The ministry said 59 people were in hospital, 10 of them in intensive care.

Deputy General Prosecutor Sergei Fridinsky said late on Friday the blast could have been an act of revenge by Chechen separatists involved in a decade of on-off warfare because servicemen hurt in Moscow's crackdown against rebels were treated at the hospital.

"Judging by the scale of the destruction and the number of people in the hospital -- 150 people, including 100 patients and 50 staff -- the number of victims is likely to rise," he told Russia's Interfax news agency.

Salambek Maigov, envoy for the rebels, told Interfax exiled separatist Chechen President Aslan Maskhadov had nothing to do with the blast at the hospital.

"I take full responsibility in declaring that neither Aslan Maskhadov nor the (separatist) leadership are involved in this explosion," he said.

Maskhadov was elected in 1997 during a period of de facto independence for Chechnya, but chased from power when Russia launched a new crackdown against separatists in 1999.

The blast appeared to be the most deadly attack in Russia since 59 people were killed when two suicide bombers drove a truck bomb into an administration building in Chechnya in May.