Gunmen fired automatic weapons and grenades inside an upmarket shopping mall in Kenya's capital Nairobi on Saturday, killing at least 30 people and injuring more than 50, the Kenyan Red Cross said, dpa reported.
Kenya's government pegs the death toll at 11.
Gripped by fear and panic, hundreds of shoppers streamed out of the Westgate mall, some carrying young children, some bleeding heavily. They cowered behind parked cars and hid behind walls for protection.
"They threw a grenade. They were showing us Arabic writings. If you could read it, you were safe. If you could not read it, they would shoot you," a witness told dpa.
"One of them shouted, 'Today, you will know the al-Shabaab in their true colours'" he said. Al-Shabaab is a Somali Islamist militant group with ties to al-Qaeda.
However, two South African survivors told dpa the gunmen spoke in Kiswahili, a language commonly spoken in Kenya.
The Interior Ministry said in a statement: "We confirm there are armed criminals but we haven't established who they are."
It was still too early to speculate on the motive of the attack, a government spokesman Manoah Esipisu said.
Since the attack began in the late morning, the government has tightened security across Nairobi.
Mutea Iringo, the principal secretary of the interior ministry, said security forces were searching for gunmen still in the building and working to "bring this matter under control."
By the evening, the scene outside the mall remained chaotic. Sporadic gunfire could be heard, even after special police units had entered the building in an attempt to rescue those still trapped.
An anti-terrorist squad and hostage rescue team were inside, as well as the military. A police source told dpa 18 gunmen had entered the mall.
Defence Department deputy director Bogita Ongeri told dpa that air force planes were dispatched.
Westgate is a wealthy Nairobi neighbourhood where many United Nations workers and diplomats reside, often frequenting the mall on weekends.
"I was shot, terrified and not knowing what to do, I crawled on the floor, a Swiss man, named Andrew, who was behind me, was shot in the chest ... Another woman, who was with us was shot. She died," one witness told dpa.
The attackers also stormed a children's cooking competition inside the mall that was being hosted by a local radio station. Well-known radio host Ruhilla Adatya was killed.
"There was a loud bang. I thought the building was coming down. I took cover under a car. I saw four men, very young men, with a lot of ammunition strapped to their waist," Chris Wamalwa, one of those inside, told dpa.
"They shot four men before my eyes. One of them, an Indian couple, was driving out of the basement. They shot at the man. He fell out of the car. I was later evacuated through an emergency exit of the parking lot," Wamalwa said.
Seven hostages were taken while shopping at the Nakhumatt supermarket chain inside the mall, but the chain's management said the gunmen made no demands.
In Washington, the State Department condemned the "senseless" attack.
"We condemn this senseless act of violence that has resulted in death and injury for many innocent men, women, and children," State Department spokeswoman Marie Harf said. "Our condolences go out to the families and friends of all victims."