As terrified residents scattered into bushes in Baga town and surrounding villages, the gunmen unloaded motorcycles from their trucks and followed in hot pursuit.
Residents hid under scant brush. Bullets pierced them.
Some sought refuge in their homes. They were burned alive.
Many who tried to cross into neighboring Chad drowned while trying to swim through Lake Chad.
By the time the weapons went quiet, local officials reported death tolls ranging from hundreds to as many as 2,000 people.
That was January 3, nine days ago.
On Monday, bodies still littered the bushes in the area.
"It is still not safe to go and pick them up for burial," said Musa Bukar, the chairman of the local government where Baga is located.
No emergency crews will enter the villages where militants are still running amok, local authorities said.
"Baga is not accessible because it is still occupied by Boko Haram
," said Sen. Maina Ma'aji Lawan of northern Borno state.
The strategic Nigerian town borders Chad, giving the extremists better access to both countries.
Boko Haram has terrorized northern Nigeria regularly since 2009, attacking police, schools, churches and civilians, and bombing government buildings. The Islamist group has said its aim is to impose a stricter form of Sharia law across Nigeria, which is split between a majority Muslim north and a mostly Christian south.
The group's brutal tactics have shocked and stunned the world.
It has kidnapped students, including more than 200 schoolgirls who were abducted in April -- and remain missing.
On Saturday, explosives strapped to a girl
detonated at a crowded marketplace in Nigeria, killing at least 20 people. Although no one has claimed responsibility, Boko Haram militants are the main suspects.
But the scale of the early January attack -- the death of hundreds, possibly thousands -- defies belief.
The attacks started at dawn on January 3 and continued throughout the weekend, according to residents.
"Each new crime committed by Boko Haram exceeds the last in brutality. This is a direct consequence of the environment of total impunity in which Boko Haram operates. Every time they get away with mass murder, rape and the enslavement of women and children, they are emboldened," Angelina Jolie, special envoy of U.N. High Commissioner for Refugees, said in a statement.
She urged the United States and other nations to offer Nigeria help to "collect evidence and bring the perpetrators of these attacks to justice."
Amnesty International called the massacre Boko Haram's "deadliest act."
"If reports that the town was largely razed to the ground and that hundreds or even as many as 2,000 civilians were killed are true, this marks a disturbing and bloody escalation of Boko Haram's ongoing onslaught," said Daniel Eyre, Nigeria researcher for Amnesty International.
The Nigerian military said the description of the attack as "the deadliest" was "quite valid."
"The attack on the town by the bloodhounds and their activities since January 3 should convince well meaning people all over the world that Boko Haram is the evil all must collaborate to end," it said.
Stranded on an island
The misery is far from over.
Those who survived the attack and tried to swim to Chad are now stranded on Kangala Island on Lake Chad.
Chadian authorities are asking the United Nations to help relocate more than 1,000
Abubakar Gamandi, a native of Baga who was away during the attack, said those trapped there are dying.
"I have been in touch with them on the phone," he said. "They told me some of them are dying from lack of food, cold and malaria on the mosquito-infested island."
Of the 30,000 people displaced during the attacks, 20,000 camped in Maiduguri city. An additional 10,000 were being ferried from Monguno town, which is about 60 kilometers (36 miles) from Baga.
Troops in pursuit
Mike Omeri, a national security spokesman, said Nigerian troops are pursuing the militants.
"Security forces have responded rapidly and have deployed significant military assets and conducted airstrikes against militant targets," Omeri said. "Troops are engaged in operations to reclaim the area from the terrorists."
But Gamandi, the Baga native, said it's not true.
"From information we are receiving from residents nearby, not a single Nigerian soldier has shown up in Baga since it was seized by Boko Haram," he said. "It is all propaganda."
Critics have accused President Goodluck Jonathan's government of not doing enough to address the insurgency, which mostly affects opposition strongholds.
Nigeria is holding presidential elections next month. Last week, Jonathan launched his re-election bid in a raucous rally in Lagos.
He did not say a word about the massacres.