Mr. Bilal said he had counted nine vehicles — two were land cruisers with machine guns on top — filled with fighters in military uniforms. He ran away with several students and colleagues, he said, but 30 minutes later returned to gather other students to help them flee.
“We were so afraid, but we didn’t want to leave them,” he said.
Government officials in Yobe State, where Dapchi is, said on Wednesday that they had no credible information that the girls had been taken hostage. They were continuing to receive reports that some missing girls had been found safe, they said in a statement.
“His Excellency, Gov. Ibrahim Gaidam, is deeply saddened and outraged by the unfortunate event and has directed that all relevant personnel and agencies work closely with the army and other security organizations,” the statement said.
Later in the day, President Muhammadu Buhari released his own statement, saying on Twitter that he had directed the military and the police to mobilize to find the missing girls. He said the defense minister would also lead a delegation to Yobe State on Thursday to “ascertain the situation.”
“I share the anguish of all the parents and guardians of the girls that remain unaccounted for,” Mr. Buhari said. “I would like to assure them that we are doing all in our power to ensure the safe return of all the girls.”
Mr. Bilal said that he and others were able to help about 300 girls climb over the fence around the school’s perimeter. One teacher’s wife miscarried during the attack, and the teacher broke his leg trying to flee, Mr. Bilal said.
Mr. Bilal said parents had been arriving at the school looking for their daughters. “It’s an awful situation,” he said.
Adding to the confusion was the difficulty reaching some families to confirm that their daughters had turned up at home; some live in areas with poor phone networks. The school has closed for the week to assess the situation.
The statement on Wednesday from the Yobe government, more than two days after the attack, was the first time officials remarked publicly about the incident.
The long silence stoked fears, largely because it echoed a similar lack of communication in the days following what turned out to be the abduction of nearly 300 girls from a secondary school in the village of Chibok, in an adjacent state, in April 2014.
Senator Ben Murray-Bruce, in a tweet, said the situation in Dapchi “should be handled better.”
“I have a terrible sense of Déjà vu,” he wrote. “We can’t allow this to happen again.”
Oby Ezekwesili, a former education minister and founder of the Bring Back Our Girls organization, which has been fighting for the release of the Chibok students, criticized the government on Twitter, saying that officials had been “ominously mum” about the Dapchi school attack. It took the government two days to release an official statement.
It took a number of days after the students in Chibok were taken to mount any concerted effort to find them, Ms. Ezekwesili said. The slow response, she said, allowed militants to escape with many young girls.
Last year government officials negotiated for the release of about half of the missing students from the Chibok kidnapping. Several others escaped their captors. And earlier this month, officials secured the release of a group of police officers and university professors who were kidnapped by Boko Haram last year.
Several high-level Boko Haram commanders were also released last year as part of a prisoner swap in exchange for hostages, and millions of dollars was paid to militants as ransom.