Suspected Somali militants from Al-Shabaab are believed to be behind the attack at a Dusit office hotel and office complex located at the riverside area.
Security officers are currently engaged in a fierce fight with armed gunmen who are holed up at the Dusit hotel.
The fighting commenced following a massive blast that could be heard some five kilometres away.
According to eyewitnesses, gunmen stormed the hotel and started firing at bystanders, and a blast suspected to be caused by a bomb immediately rocked the area.
At the time of filing this report by 6:31 pm (Kenya time) armed gunmen could be seen engaging security officers at the Dusit hotel, mainly patronized by middle and upper class Kenyans.
No government or security official has so far commented on the attack.