A Nigerian official says gunmen shot dead at least 17 worshippers who had attended a church service to usher in the new year.
The chair of a local community group, Osi Olisa, said Tuesday that the gunmen also shot people on the road before escaping.
No group has claimed responsibility for the attack in Omoku, about 88 kilometres northwest of the capital city of Rivers State, Port Harcourt.
Suspicion has fallen on an armed group believed to be behind kidnappings and killings in the area. In November, local defence groups and security officials shot dead the group's leader.
Gun violence is common in parts of Nigeria's oil-producing Niger Delta region, where various militant groups take up arms against multinational companies to demand a share of the oil proceeds.