The Somali army is attempting to retake the hotel after militants detonated a car bomb and stormed it, police said.
Reports said the victims included three security guards.
Al-Shabab militants frequently carry out attacks in the city in their bid to topple the Western-backed government.
The al-Qaeda-linked group said it targeted the hotel which was “frequented by the apostate government members”, Reuters news agency reported.
The Naso-Hablod, in southern Mogadishu, is often used by politicians and tourists.
It is not known how many attackers entered the hotel nor how many guests were inside.
A witness told the Associated Press news agency the gunmen shot randomly at guests.
At least 10 other people have been wounded.
Earlier this month at least 10 people were killed and 50 injured in an attack on another hotel in Mogadishu, which was claimed by al-Shabab.
The group was driven from Mogadishu in 2011 but still remains a threat and frequently carries out attacks in the city.
The Somali government, with the help of African Union forces, is fighting al-Shabab militants in several parts of the country.
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