Three people were confirmed dead in the 14 Riverside Drive attack in Westlands on Tuesday.
Police have quelled the fire and people are being evacuated.
Officers at the scene said the attackers came with a vehicle wearing a bulletproof vest ready to attack.
"Several hostages have been held in Dusit hotel and we are waiting for back up," the officer told the Star.
Students from the University of Nairobi have been evacuated at the Chiromo building as the operation continues.
Check photos below.
Below are photos of the situation on the ground.
