A Somali police official, General Mohamed Yusuf Madale, told reporters the car bomb went off outside the Golden Hotel shortly after midday, "killing at least one person and injuring another one".
"The car belongs to a young man who lives in the hotel and now he is under arrest. Investigations are going on," he said.
He did not identify the person killed, but Somali news reports said it was a telecoms official.
There was no immediate claim of responsibility, although similar attacks have been carried out in the past by Somalia's Al-Qaeda-affiliated Shebab rebels, who are fighting to overthrow the country's internationally-backed government.