Seventy-three-year-old Nadezhda Pavlovna was in bed when the windows of her apartment blew in and a lamp flew across the room, striking her leg. She thought at first an earthquake had struck.

"My daughter screamed 'Quick we have to get out of here. The house is going to fall down,'" she recalled. "We ran downstairs. There was so much smoke and a terrible smell. I couldn't breathe and people were upset and panicking. Many people were covered in blood."

Sitting in her nightshirt outside the ruins of the building where she once lived, Nadezhda was glad to be alive.

At around midnight Wednesday, a powerful blast ripped apart her nine-story Moscow apartment building, killing at least 84 people and injuring hundreds of others.

Vladimir Legoshin, deputy director of the Emergency Situations Ministry rescue division, said dozens of people remained trapped under the rubble and there was little hope they could have remained alive as the wreckage had been consumed by fire and a choking smoke, which had hampered rescue efforts.

He did not rule out the possibility of a terrorist act.

"It was one of the strongest explosions I've seen," he said. "It could have happened inside or outside the building, although more than likely inside."

A Russian Red Cross spokesman said the fire in the building had reached class five - the worst possible. He called it the biggest disaster to hit Moscow in a long time.

Valery Nikolayev said his friends and their child, who was his daughter's friend, had been killed in the blast.

"They're not on any of the lists of the survivors or the dead. This means they are still there missing under the ruins," she said. "I spoke to them the day before and everything was okay. Now they are gone and there is nothing left.

"They lived in the fourth entrance to the building on the eighth floor. I went to have a look and understood that they were dead. Their whole section of the building was completely destroyed. Even if they were buried they would not be able to breathe because of the fire and smoke. I don't know what to tell my daughter."

A shocked Kostya, who would not give his last name, said his brother, his brother's wife and their three-and-a-half-year-old daughter were all dead.

"I heard on the news the house had fallen down and came straight here," he said. "I can't get any information about my relatives. They don't say which morgue [they may be in]. I want to know if they got them out. They lived on the fourth floor, so it seems unlikely."

At least 368 people were evacuated from the building and rescue workers said they had pulled at least sixty survivors from the wreckage.

Yuri Petrovich, 53, who suffered cuts and bruises, said all his windows had shattered and furniture near the windows flew into the middle of the room.

"My wife started to panic and demanded we leave the building," he said. "I looked from the balcony and saw that the next entrance to the building was completely missing. I went onto the street and saw the fourth and fifth entrance were missing. I can imagine how awful it would be to be buried under there."

Tamara Mikhailovna Filimonov, 73, was hit by glass. Her disabled husband and granddaughter were taken to hospital after suffering glass cuts.

"The door blew in and I screamed. I thought it was the end of the world," she said. "We were scared. We did not know where to go. It was night and everything was dark."

Speculation has mounted about the cause of the blast. Prime Minister Vladimir Putin said a natural gas explosion apparently caused the incident. However, the Federal Security Service said the nature of the incident and the number of casualties suggested an explosive device had been used.

Moscow Mayor Yury Luzhkov, who visited the scene, said the blast was a terrorist act, Interfax reported. He said 63 people had died and 43 remained in hospital, two of them in a serious condition, by Friday morning.

Luzhkov said an explosive substance called hexogen had probably been planted in an empty office on the first floor of the building, rented by a company called Delko-2.

Security measures in the city would be stepped up as a result of recent incidents, Interfax reported Luzhkov as saying, while he called on citizens and police to be extra vigilant.

The blast is the fourth major explosion to hit the country this year. A bomb at the Manezh shopping center, near the Kremlin, killed one woman and injured more than 40 last week, and a car bomb devastated an apartment building for military officers and their families in Buinaksk, Dagestan, killing 64 people days later.

Eleven people were also killed when an explosive device went off in Moscow's Intourist Hotel last April.

The latest explosion was heard for miles. Concrete and glass rubble were strewn 100 meters from the explosion site and shock waves from the blast mangled cars and blew out windows from the neighboring block.

Many residents felt the explosion was too powerful to have been caused by gas and claimed they did not smell gas when they ran out onto the streets from their buildings.

Others speculated that something could have detonated inside one of the first floor shops or that the incident was the work of a criminal organization.

Political groups expressed sympathy for relatives and friends of victims and called on the state to better protect its citizens. They demanded an open investigation to be held into the explosion.

Residents made homeless by the blast were promised accommodation in hostels and hotels by Lyudmila Bazhenova, leader of the Pechatniki Social Services Center.

She said building 17 would be repaired and the fate of building 19, where the explosion occurred, was still to be decided. Residents of destroyed homes would be paid compensation for the loss of family members, funeral costs and for loss of property, she added.

Earlier in the week, the Moscow correspondent of Deutsche Welle, Germany's international broadcasting service, received a call from a man claiming there would be three explosions in Moscow. He said they would be "an act of revenge for the bombing of Chechen villages by the Russian army," Deutsche Welle reported.

An anonymous caller later told Interfax that the apartment explosion and bomb blast in Buinaksk, Dagestan, were in response to Russia's military campaign against Islamic rebels in Dagestan.