At least three attackers were involved, some of them female, witnesses said. More than 30 people were injured.
It is not yet known who was behind the attack.
But suspicion is likely to fall on militants from the Boko Haram Islamist group, who abducted more than 200 schoolgirls from Chibok in 2014.
A town elder warned that the death toll could rise.
"The situation is now tense and there's so much confusion. It will take some time before we can be able to have a clearer picture of the casualties," Ayuba Chibok told the AFP news agency. Read more on bbc.