MAIDUGURI, Nigeria - Hospital and local residents on Tuesday said 20 people may have been killed in another attack on students and fishermen by the Boko Haram insurgents in the Nigeria northeast Maiduguri city currently under a state of emergency.

"Thirteen fishermen and tea sellers have been killed at Alau River. Gunmen numbering about five stormed the river area and opened fire on fishermen at the river bank and two local tea seller today," a resident told Xinhua.

A competent military source also said the insurgents invaded a private school, Ansaruden Private Primary and Secondary School at Jajeri, a Maiduguri suburb and opened fire on the students who were writing their national examination - National Examination Council (NECO).

"Nine of the students were shot dead by the insurgents while many of them were injured," a military officer disclosed on condition of anonymity.

Hospital sources said about 20 corpses with gun shots were brought to the State Specialists Hospital on Monday evening but did not give details of the age categories of the deceased.

Spokesman of the JTF Lt Col Sagir Musa was not reachable for comment.

On May 14, Nigerian President Goodluck Jonathan declared a state of emergency in the northern states of Adamawa, Yobe and Borno following waves of killing and attacks by Boko Haram suspects. The three states share borders locally and international borders with African countries Cameroon, Chad and Niger.