Nairobi mall siege
Customers dive under tables as the siege begins (Arjen Westra/Twitter)

The armed gunmen who attacked the Westgate shopping mall in Nairobi, Kenya, on Saturday told Muslims to leave, saying that non-Muslims would be targeted, say witnesses.

Elijah Kamau said that attackers with AK-47s and grenades made the statement as they began their attack at the Westgate shopping mall in Kenya's capital, at around midday.

Gunmen threw grenades and opened fire during the attack.

The Kenyan Red Cross has reported at least 15 people are dead, with many more injured. Meanwhile, several shoppers in the upscale shopping mall, which is in a wealthy enclave of Nairobi, have been taken hostage by the gunmen, who are believed to be connected to the Somali insurgents, al-Shabaab.

Officials did not give an official death toll but witnesses have reported seeing 50 dead and injured.

Nairobi police chief Benson Kibue said this was a terrorist attack and that there are probably no more than 10 terrorists involved, as gunfire continues to be exchanged.

Manish Turohit, 18, says he saw gunmen with AK-47s and vests with hand grenades on them inside the mall. He escaped after hiding in the parking garage for two hours.

A group of people remain in hiding inside the mall.

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 Islamic insurgents.

Al Shabaab militants
Al-Shabaab militants display their weapons (Reuters)