Thousands of Venezuelans have rushed to border crossings with Colombia after Colombian President Juan Manuel Santos announced a tightening of controls.
Only those who have registered for a special border card or can produce a passport will be able to cross.
They fear it will become more difficult for them to enter Colombia once the measures are fully implemented.
Thousands of Venezuelans cross into Colombia daily to look for temporary work or to buy essential goods.
Most of them return home, but the Colombian government expects many more to stay permanently as Venezuela’s economic crisis worsens.
Brazil has also expressed concerns, with thousands of Venezuelans are living in precarious accommodation in the border state of Roraima.
Nicolás Maduro, who has been in office since 2013, is running for a second six-year term. He says the crisis has been caused by economic sabotage sponsored by the US.