More than 4,000 people have crossed into The Gambia after fighting between Senegal's army and rebels in the southern Casamance region, the UN says.
The chief of Gambian border village Gifanga said they were unable to house any more refugees and asked for help.
A UN spokesman in The Gambia said food supplies had also run out.
The Senegalese government launched an offensive against a splinter group of the MFDC rebels near the Gambian border last week.
There are some 12,500 Senegalese refugees in The Gambia, the UN refugee agency, UNHCR, says.
Separatists from a faction of the Movement of Democratic Forces of Casamance (MFDC), led by hardliner Salif Sadio, began a new campaign against government forces earlier this year.
Mr Sadio has refused to join other rebel factions in peace talks with the Senegalese authorities and continues to campaign for the independence of Casamance.
The Gambia lies between Casamance and the rest of Senegal.