The blast - caused by explosives concealed in a crop-spraying backpack - ripped through the weekly market in the village of Sabon Gari, around 135 kilometres (85 miles) south of Borno state capital Maiduguri, during peak trading today.
The Nigerian military described the attack as a "suicide bombing" although no local authorities have confirmed this and witnesses said the bag had been "abandoned" before it exploded.
"When the blast happened, people in the market fled in fear. They abandoned their wares. Some managed to return for their wares but some never came back," Samaila Biu, a local trader, told AFP.
The explosion occurred around 1:15 pm (local time), during the market's most busy trading hours when the area was packed with merchants and shoppers, Biu said.
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In the immediate aftermath, officials said 47 people had been killed but upped the toll by three overnight.
"One more person died from his wounds and two more bodies were later brought to the morgue from near the scene of the blast. Now there are 50 dead and 51 injured," a nurse at Biu General Hospital, around 50 kilometres (30 miles) away, told AFP.
"We believe they managed to flee the scene with injuries from the explosion but died on the way," he told AFP.
Dozens of soldiers today formed a security ring around the market, which was littered with footwear and clothing and still spattered with congealed blood.
They were also patrolling the nearby streets.
"The village is still in shock although most of the victims were from other places far and near who came to attend the market," Bura said.
No one has claimed responsibility for the attack but witnesses said the blast bore the hallmarks of Boko Haram, which has previously targeted crowded bus stations, markets, mosques and churches during its bloody six-year insurgency.