At least 27 people, including two children, have been killed and 53 others wounded in southern Somalia when mortar shells exploded, a local official and state media said.

Abdi Ahmed Ali said on Friday that a blast "caused by unexploded mortar shells" occurred near the town of Qoryoley, around 120 kilometres south of the capital, Mogadishu.

He requested help from the authorities to clear unexploded ordnance he said was scattered across the region in order to avoid further disasters.

Qoryoley resident Ibrahim Hassan told the AFP news agency most of the victims were "young children" who "died on the spot after one of them struck an explosive device near a playground".

The region is a target of Al Shabab terror group, which has waged an insurgency against the internationally backed Somali federal government since 2007.

Last month, the group affiliated with Al Qaeda killed 54 Ugandan peacekeepers in an attack on an African Union base in Bulo Marer, a town around 30 kilometres from Qoryoley.

The group has been driven out of Somalia's main towns and cities but retains power in large swathes of rural areas, carrying out attacks against security and civilian targets.