The hotel chain said two armed men have locked in 140 guests and 30 employees.
Malian soldiers with help from U.N. troops have the hotel surrounded.
No group immediately claimed responsibility for the incident.
“This week there was a big delegation for the peace process at the Radisson hotel in Bamako,” said Olivier Saldago, a spokesman for MINUSMA. MINUSMA is the U.N. mission in the nation.
The United Nations sent peacekeepers to Mali in 2013 to guard against militant Islamists who threatened to move on Bamako.
In August, 12 people — including five Malian soldiers — were killed in a hostage situation and ensuing battle at a hotel in Sevare in central Mali.
The soldiers stormed the hotel to end a daylong siege that started when gunmen raided the hotel after attacking a military site nearby, witnesses said.
In that incident, the attackers were affiliated with the Macina Liberation Movement.
Human Rights Watch has described the group as Islamists who commit “serious abuses in the course of military operations against Mali’s security forces.”