The quake, with a preliminary magnitude of 6.8, struck at 2:20 p.m. (7:20 a.m. EST) and was centered beneath Lake Tanganyika on the Congo-Tanzania border, about 600 miles southwest of Nairobi, Kenya, the U.S. Geological Survey said on its Web site.
"Dozens of houses have collapsed, several children were buried by the roofs of their houses," said Dr. Jean-Donne Owali, a Congolese humanitarian worker in the lakeside city of Kalemie, Congo, about 35 miles from the epicenter.
Owali said at least two people had died of injuries at his clinic. He said he saw children bleeding from head injuries after their mud-and-thatch homes collapsed.
U.N. spokesman Michel Bonnardeaux said a child was killed in the city when two houses and a church "crumbled." Three people were wounded. It was not immediately clear if the child was one of the two people Owali reported killed.
Bonnardeaux said most of the injuries in the area were from falling zinc and steel roofs. The desperately poor region also has camps for tens of thousands of refugees from wars and economic collapse in Congo and Burundi.
The quake sent panicked people running from buildings in Kigoma, the main Tanzanian transport hub on the shores of Lake Tanganyika about 90 miles from the epicenter, said regional commissioner Elmon Mahawa. Authorities were waiting for police stations in remote parts of the country to report on any casualties.
The USGS said the quake was located about six miles underground and shook Nairobi and the Kenyan coastal city of Mombasa. It was also felt on the shores of Lake Victoria, Africa's largest lake, and in Tanzanian towns bordering Zambia and Malawi, Tanzania's meteorological chief Mohamed Mhita said by phone from the commercial capital of Dar es Salaam.
Henri Burgard, U.N. spokesman in the Congolese town of Uvira, said the quake lasted 30 seconds. "The buildings shook quite strongly. We have no reports of deaths so far," he said.
In Bujumbura, the capital of Burundi, an Associated Press reporter felt a three-story building sway in two waves of the quake.
The region is located along the Great Rift Valley, which runs for 3,000 miles between Syria and Mozambique. In January 2002, a volcano erupted along the fault in eastern Congo, forcing some 300,000 people to flee and destroying the homes of 120,000. An estimated 100 people were killed.