NAIROBI, Kenya (CBS) -- Gunmen threw grenades and opened fire Saturday killing at least 10 people in an attack targeting non-Muslims at an upscale mall in Kenya's capital that was hosting a children's day event, witnesses said.
A local hospital was overwhelmed with the number of wounded being brought in hours after the attack, so they had to divert them to a second facility.
Elijah Kamau, who was at the mall at the time of the midday attack, said that the gunmen made a declaration that non-Muslims would be targeted.
"The gunmen told Muslims to stand up and leave. They were safe, and non-Muslims would be targeted," he said.
Manish Turohit, 18, said he saw gunmen with AK-47s and vests with hand grenades on them inside the mall before he escaped to hide in a parking garage for two hours.
"They just came in and threw a grenade. We were running and they opened fire. They were shouting and firing," he said after being marched out of the mall in line with about 15 people who held their hands in the air.
Rob Vandijk, who works at the Dutch embassy, said he was eating at a restaurant inside the mall when attackers lobbed hand grenades inside the building. He said gunfire then burst out and people screamed as they dropped to the ground.
It appears the attack began at the outdoor seating area of Artcaffe at the front of the mall, witnesses said.
Patrick Kuria, an employee at Artcaffe, said: "We started by hearing gunshots downstairs and outside. Later we heard them come inside. We took cover. Then we saw two gunmen wearing black turbans. I saw them shoot."
Some people were shot at the entrance to the mall after volleys of gunfire moved outside and a standoff with police began. Ambulances continued to stream in and out of the mall area, ferrying the wounded who were gradually emerging from hiding inside the mall.
Many of those running from the mall clutched small children. Others were crying. Mall guards used shopping carts to wheel out wounded children.
Associated Press journalists at the mall said they saw at least 10 dead bodies and dozens wounded hours after the attack began. Officials did not yet give an official death toll.
"We are treating this as a terrorist attack," said police chief Benson Kibue, adding that there are likely no more than 10 attackers involved. Gunfire continued to be exchanged outside the mall, as a group of people remained in hiding inside the building.
Police did not say what group was responsible for the attack.
Somali's rebel group al-Shabab vowed in late 2011 to carry out a large-scale attack in Nairobi in retaliation for Kenya's sending of troops into Somalia to fight the Islamic insurgents.
The Westgate Mall is situated in Nairobi's affluent Westlands area and is frequented by expatriates and rich Kenyans.