The government said the west African country suffered a "tragedy" yesterday, a day after Guineans celebrated the Eid al-Fitr holiday ending the Muslim fasting month of Ramadan.
The authorities gave no details on how the stampede occurred on Rogbane beach in the city's northern Ratoma suburb where popular Guinean rap group "Instinct Killers" was playing among other artists.
Medics took at least 24 bodies including 13 girls to a hospital morgue at Donka, a hospital official told AFP.
The president's office said in a statement it was "shocked by the tragedy caused by (crowd) movements at a cultural event".
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It said there were dead and injured but did not give a toll. "A week of national mourning has been decreed from this day," it added.
An investigation has been launched to determine what caused the stampede. The official in charge of organising such events was suspended.
At least two people were killed and 25 injured when fans stampeded at a concert given in Guinea by popular local musician Sekouba "Fatako" Kouyate on December 18, 2001.
Similar tragedies have marred musical events around the world.
A stampede at a world music festival in Rabat, Morocco in May 2009 left at least 11 people dead and some 40 others injured.
Ten people, mostly teenagers, were killed and dozens injured in a stampede at a packed music concert in Indonesia's Central Java province in December 2006.
In October 2005, 11 people were crushed to death and around 60 injured in South Korea in a stampede before a pop concert in the southern city of Sangju.
And in one of the deadliest such incidents on record, in May 1999, 52 people, mostly young women, were trampled to death after a rock concert in Belarus, authorities said.