A suicide bomber blew himself up inside the main police academy in Somalia's capital Mogadishu on Thursday with several people feared dead, police said.
Witnesses said the police were gathering for their early morning parade, and were crowded in an open square when the bomber attacked.
"A man wearing an explosive vest entered the camp disguised as a policeman, and blew himself up," police officer Mohamed Abdulle said. "There are casualties, and many injuries."
Abdulle did not immediately have a toll for the number killed but said he feared there could be several dead.
"Medical rescuers are still working on evacuating the casualties," Abdulle said.
The police camp is Somalia's biggest police academy.
"Some of the police were already in lines, and others were gathering, when the man in police uniform entered and blew himself up," said bystander Hussein Ali. "Ambulances have been rushing the wounded away and taking the dead bodies."
There was no immediate claim of responsibility for the attack.
However, the Al-Qaeda-affiliated Shabaab has repeatedly attacked police officers in its decade-old battle to overthrow successive internationally-backed governments in Mogadishu.
The Shabaab lost its foothold in Mogadishu in 2011 but has continued its fight, launching regular attacks on military, government and civilian targets in the capital and elsewhere.