There is constant traffic between Nigeria and Niger
Nigerian customs officials are blocking Niger from importing goods, Niger's foreign affairs ministry has confirmed.
The reason for the interruption of cross-border trade, which began on Tuesday, is not known.
A BBC reporter at a border crossing says there are lines of trucks waiting to cross into Niger and only people with a few loaves of bread can pass.
Nigeria's government has denied that it ordered the border to be closed and has not commented on the border hold-ups.
People travelling south from Niger into Nigeria along the 1,500km (940 mile) border are not affected.
The BBC's Chima Ila at the Nigerian crossing point to Maradi State in Niger said truck owners were angry.
Many travellers from Niger were also unhappy at the situation, as many along the border are reliant on food from Nigeria, she said.
Niger was suspended from West Africa's trade bloc Ecowas last month after President Mamadou Tandja went ahead with a controversial parliamentary election.
But its neighbours stopped short of measures such as trade embargoes.
Earlier this year, Mr Tandja dissolved parliament and had the constitution changed to let him seek a third term.
The land-locked, arid and drought-prone country depends on its giant neighbour for many of its imports.