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The source, who spoke on condition of anonymity, said the bloodiest attack happened in the village of Konkoso, where at least 38 people were shot dead or had their throats slit.
Most of the homes in the village were burned down and apart from those already counted as dead, “other bodies are being recovered,” the source added.
The raids by gunmen happened in villages in the Borgu local government area in Niger State, on the border with Kwara and Katsina states, a humanitarian source told AFP news agency on Saturday.
Armed men shot locals dead, set homes alight and abducted an unknown number of people in Niger State, Musa Saidu, head of the State Emergency Management Agency (Sema), told the BBC.
The attacks on Saturday morning occurred near the site of a suspected jihadist massacre earlier this month, in which more than 100 people were killed in a similar ambush.
Armed criminal gangs, known as bandits, have carried out attacks and kidnappings in Nigeria for years, mainly targeting those in the north-west - but reports of attacks in other parts of the country have risen sharply more recently.
Bandits swooped on the village of Tunga-Makeri early in the morning, before striking the nearby villages of Konkoso and Pissa, local officials said.
Police said six people were killed in one incident, and 20 more in the attacks on Konkoso and Pisa.
Officials confirmed at least 29 people had been killed as of Saturday, but Saidu said that death toll could rise.
The number of people abducted is also unknown because many residents fled their homes and ran into the nearby bush or neighbouring communities, he said.
"People are afraid because you can't tell which community is going to be next," he added.
A security report cited by AFP news agency said bandits came on 41 motorcycles, each carrying two or three men.
Abdullahi Rofia, a resident of neighbouring Agwara, told the BBC that many displaced people have taken shelter in his community, which was itself attacked two weeks ago.
"People are so traumatised, they no longer go to farm nor do they go to market," he said.
"The bandits are not interesting in stealing or looting - they are more interested in killing and terrorising locals."
Authorities have introduced emergency measures, including a restriction on late-night gatherings and a "partial curfew" that bans motorcycle taxis from operating after 20:00 local time (19:00 GMT).
Police confirmed that security teams have been deployed and rescue efforts are ongoing.
Nigeria's leaders are under pressure to curb violence, with jihadist groups active in the north-west and separatist insurgents based in the country's south-east.
The US launched Christmas Day strikes targeting Islamist militants in Nigeria's northern Sokoto state and President Donald Trump warned of further attacks "if they continue to kill Christians".
Many of the victims of jihadist violence are Muslim, according to organisations monitoring political violence in Nigeria.
A Nigerian official told the BBC last month that 200 suspected bandits had been killed in an operation in the central Kogi state.
It came after more than 250 children and staff were abducted from a Catholic school in Papiri, in one of the largest recent mass-kidnappings. Their release was later secured.