The sound of automatic guns being fired could be heard many miles away from the place under attack says journalists.
According to security sources "the gunmen were 'jihadists' who had entered the hotel compound in a car that had diplomatic plates."
"It's all happening on the seventh floor, jihadists are firing in the corridor," one security said.
According to Associated Press: Malian soldiers, police and special forces were on the scene as a security perimeter was set up, along with members of the UN's MINUSMA peacekeeping force in Mali and the French troops fighting jihadists in west Africa under Operation Barkhane.
The Rezidor Hotel Group, the US-based parent company of Radisson Blu, said two people were holding 170 people hostage.
The company said it was "aware of the hostage-taking that is ongoing at the property today, 20th November 2015. As per our information two persons have locked in 140 guests and 30 employees".
It added in a statement: "Our safety and security teams and our corporate team are in constant contact with the local authorities in order offer any support possible to reinstate safety and security at the hotel."
- Attacks despite peace deal -
The shooting at the Radisson follows a nearly 24-hour siege and hostage-taking at another hotel in August in the central Malian town of Sevare in which five UN workers were killed, along with four soldiers and four attackers.
Five people, including a French citizen and a Belgian, were also killed in an attack at a restaurant in Bamako in March in the first such incident in the capital.
Islamist groups have continued to wage attacks in Mali despite a June peace deal between former Tuareg rebels in the north of the country and rival pro-government armed groups.
Northern Mali fell in March-April 2012 to Al-Qaeda-linked jihadist groups long concentrated in the area before being ousted by an ongoing French-led military operation launched in January 2013.
Despite the peace deal, large swathes of Mali remain beyond the control of government and foreign forces.
The website of the Radisson Blu in Bamako says it offers "upscale lodging close to many government offices and business sites", serving as "one of the city's most popular conference venues" with "a stunning 508-square-metre ballroom and meeting rooms."
Radisson Blu, an upscale brand of the Radisson hotel chain, has more than 230 luxury hotels and resorts worldwide.