Eight vehicles traveling between the towns of Beledweyne and Maxaas were reportedly stopped and burned by al-Shabab.
The passengers are then reported to have been killed.
Ali Jeyte, the governor of the Hiiran region where the attack took place, said children were among those killed, and that the death toll could rise.
The jihadist extremist group claims responsibility for the attack, but claims it was not aimed at civilians.
The attack comes two weeks after al-Shabab's deadly 30-hour siege on a hotel in the capital, Mogadishu.
Then 21 people were killed and 117 injured, according to the Ministry of Health.