An aerial view of thousands of Venezuelans trying to enter Colombia through the border crossing of Cucuta on the Simon Bolivar International Bridge in Cucuta, Colombia, on Friday.

Colombia and Brazil tightened border controls with Venezuela on Thursday as both nations grapple with a mounting influx of hundreds of thousands of desperate migrants fleeing a worsening economic crisis.

The moves to tighten border security could threaten a key social safety valve for desperate Venezuelans as hyperinflation and a severe recession grip their oil-rich country.