It is the fourth suicide bombing this month in Maiduguri, which is the birthplace of the Boko Haram Islamic extremist group.
Fishmonger Idi Idrisa said one teenager exploded as she approached the mosque crowded with people from the nearby Baga Road fish market, performing afternoon prayers during the holy month of Ramadan.
The second teen appeared to run away and blew up further away, killing only herself, he said.
Civilian defense fighter Sama Ila Abu said he counted at least 30 corpses as he helped collect the dead.
