An eight-story apartment building was destroyed by a powerful blast here this morning, killing at least 30 people and injuring many others. Dozens more were feared missing in what officials said was the second terrorist attack in Moscow in less than a week.

The 5 a.m. explosion rocked an area of residential high-rises in southern Moscow, throwing debris into neighboring apartment buildings. Today had been designated as a national day of mourning for victims of two other recent apartment blasts, one in the southern republic of Dagestan that killed 64 people and another Thursday in Moscow that killed 94.

Those two explosions were blamed on bombs. After surveying the damage from today's blast, Emergency Situations Minister Sergei Shoigu said it appeared very similar to Thursday's.

Russian politicians have said the two earlier bombings are related to the conflict in Dagestan, where Russia is battling several thousand Islamic guerrillas who crossed into the region from neighboring Chechnya. The Chechens' declared goal is to create an Islamic state in Dagestan, and Russia has responded with air, artillery and ground attacks on the rebels since early August.

Moscow Mayor Yuri Luzhkov said Sunday night that Thursday's bombing was "the continuation and a dislocation of the Dagestan war." In that incident, officials said highly explosive material was placed in a store on the first floor of the building. The blast sparked a large fire that hampered rescue work.

Early reports from today's scene said that there was no fire but that rescue workers were having trouble reaching the site because the building is near other high-rises that also were damaged. Police said they believed a bomb had been planted on the first floor. About 120 people lived in the building hit today, although there were no reports on how many were home at the time, police said.

The explosions have led some politicians to call for the declaration of a national state of emergency, but until now, Prime Minister Vladimir Putin and others have said it was not necessary. Some politicians also fear that the bombing campaign could have another sinister purpose, to provide a pretext for calling off December's parliamentary elections or next year's presidential campaign.