The BBC's Andrew Harding reports: "A frantic rescue operation is underway"

At least 49 bodies, including children, have been found. Dozens more may be still trapped under the rubble.

Police said a bomb was the apparent cause of the explosion, and they were treating it as a terrorist attack.

Rescuers worked through the rubble in the rain - with building debris, books and clothes flung over a wide area and left hanging in trees by the blast.

The explosion happened early on Monday morning, while most people were still asleep.

It is thought that few of the 120 people who lived in the block - situated on Kashirskoye Shosse - will have survived.

The building was flattened, with some fragments thrown up to 100m away.

The police are linking the blast to the bomb which killed 93 people in another block of flats in Moscow last Thursday.

They are looking for a man who rented premises in the two blocks.

BBC Moscow Correspondent Robert Parsons says there is a deepening fear in Russia that this is the start of a long campaign of terror.

Yeltsin blames terrorists

President Boris Yeltsin said terrorists had declared war on the Russian people.

"The bandits are operating secretly like wild animals which creep around by night, killing people who are sleeping, planting bombs in densely-populated areas, where there are many children and women and old people," he said.

"They are afraid to claim responsibility for this, concealing their names and faces, but we already know on whose conscience these evil acts lie".

BBC Moscow Correspondent Andrew Harding: "Fourth blast in two weeks"

After holding an emergency meeting with senior ministers and the Moscow Mayor, Yuri Luzhkov, he urged people to be vigilant and stay calm.

He ordered heightened security in a number of cities and at sensitive installations around Russia and called the Prime Minister, Vladimir Putin, back from the Apec forum in New Zealand.

Suspect named

Police have appealed for help in finding a man they named as Mukhit Laipanov, who they believe could also be linked to the explosion last week in south-east Moscow.

Rescuers search the wreckage for survivors

There has been speculation that both incidents were the work of Islamic guerrillas.

Chechen warlord Shamil Basayev has been leading the armed rebellion against Russian rule in Dagestan, but at the weekend he denied any involvement in the bomb attacks in Moscow and the Dagestani town of Buinaksk.

The blast is the fourth to hit Russia in two weeks.

Monday had already been declared a day of national mourning for the victims of the explosions in Moscow and Dagestan.

The latest incident happened about 6km away from site of last week's explosion.