Colombia is closing all its border crossings with Brazil, Ecuador, Panama, Peru and Venezuela on Sunday while a presidential runoff election is held.
The government say the borders will remain closed between 4am - 4pm, to enhance national security during the voting.
Nearly 30 million voters are expected to go to the polls to choose a successor to President Alvaro Uribe.
Former defence minister Juan Manuel Santos and former two-time Bogota mayor Antanas Mockus are the candidates.
Both came out ahead in the first round of votes on 30 May, but neither achieved the 50% required for an outright win.