"Police officer Mohamed Omar said the attackers "shot civilians randomly".
He said security forces killed five gunmen and a sixth member of the group "blew himself [up] at the beach".
Witnesses said there were many people at the popular location when the explosion occurred, describing how gunmen had then stormed the area.
"Everybody was panicked, and it was hard to know what was happening because shooting started soon after the blast," witness Abdilatif Ali told AFP.
He said people attempted take cover on the ground or flee.
"I saw many people strewn [on the ground] and some of them were dead and others wounded," he said.
Ahmed Yare witnessed the attack unfold from a nearby hotel.
"I saw wounded people at the beachside. People were screaming in panic, and it was hard to notice who was dead and who was still alive," he said.
Al-Shabaab has claimed responsibility for numerous bombings and attacks in Mogadishu and other parts of the country, where the government is pressing ahead with an offensive against the Islamist militants.
The Lido area has been the target of previous attacks, including a six-hour Al-Shabaab siege of a beachside hotel in 2023, which left six civilians dead and 10 injured.
Five people were killed in a powerful car bomb blast at a cafe in the capital last month.
In March, the militants killed three people and injured 27 in an hours-long siege of another Mogadishu hotel, breaking a relative lull in the fighting."
