NAIROBI, Kenya — A group of armed men attacked an upscale shopping mall in Nairobi on Saturday, killing at least 20 people, according to the Kenyan Red Cross, and wounding more than 50.
By midafternoon, police officers were swarming the mall and the gunmen were still inside, with reports that hostages had been taken.
Benson Kibue, the Nairobi police chief, told The Associated Press that it was a terrorist attack and that there were probably no more than 10 gunmen involved. Earlier, Mr. Kibue had said the attack was part of an attempted robbery.
Agence France-Presse reported that the gunmen had taken at least seven hostages, citing police and security guards at the scene. The Red Cross reported around 5 p.m. on its Twitter account that the hostages were being released, and that most hospitals in Nairobi were full.
Gen. Abbas Guled, secretary general of the Kenyan Red Cross, said in a phone interview that 20 people had been killed and over 50 wounded. The police said four people had been wounded but had not yet confirmed any fatalities.
Witnesses described hearing explosions and gunfire as they fled the premises.
Haron Mwachia, 20, a cleaner at the mall, said he escaped by climbing over a wall.
“I heard several gunshots and managed to run away,” he said. “Two of my colleagues were shot at while trying to escape the scene. There was also an explosion, which I suspect to have been a grenade.”
Vivian Atieno, 26, who works on the first floor of the mall, described “intense shooting,” starting around 11 a.m., before she escaped through a fire exit.
Stephen Opiyo, 25, who was working at a supermarket there, said: “We heard gunshots and started running, trying to find an escape route. I saw many people who had suffered gunshot injuries, and some have been taken away to hospital.”
Military helicopters hovered overhead as the police kept bystanders away from the scene.
Witnesses described attackers using AK-47 rifles and throwing grenades. Photographs from the scene showed a woman’s bloody body being lifted out of a car, the glass of the window shattered.
The police said they had surrounded the mall, and they were seen clearing the shops one by one.
“Our officers are on the ground carrying out an evacuation of those inside as they search for the attackers, who are said to be inside,” Inspector General David Kimaiyo of the Kenyan police told Agence France-Presse.
While the authorities said it was too early to determine who was behind the attack, suspicions turned immediately to the Shabab, the Somali militant group that has staged attacks in other African countries that have sent troops to Somalia to help fight the Shabab. Kenyan military forces invaded Somalia in October 2011.
In July 2010, in revenge for Uganda’s troop presence in Somalia, the Shabab killed more than 70 people who had gathered at a restaurant and a rugby field in Kampala, the Ugandan capital, to watch the final match of the World Cup.
Saturday’s attack ruptured the bubble of safety that surrounds the affluent districts of the Kenyan capital.
The United Nations uses Nairobi as a hub, and many nonprofit organizations have their regional headquarters for East Africa or even the entire continent in the Kenyan capital.
On weekends, the mall, called Westgate, is bustling with shoppers, including well-to-do Kenyans and the city’s large contingent of expatriates. Brightly lit, with peach-colored pillars, tan floor tiles and a marble stairway, Westgate has more than 80 stores covering 350,000 square feet.
Many shopping malls in Nairobi have security guards outside, checking vehicles, searching bags and using metal-detecting wands on visitors before they enter. But the guards — lightly armed if at all — would be no match for assailants armed with automatic rifles.
Westgate is in many ways like an American shopping mall, with a Converse store, a tapas restaurant and a corner where children can play while their parents shop and eat.
The United States Embassy issued a warning on Saturday after the attack, advising Americans to avoid public venues in Nairobi.
Reuben Kyama reported from Nairobi, and Nicholas Kulish from Goma, Democratic Republic of Congo. Tyler Hicks contributed reporting from Nairobi.