Increasing numbers of Venezuelans are crossing the border into Colombia to escape a worsening political crisis and economic meltdown, aid groups said on Thursday, putting more strain on social services and overcrowded shelters.
Venezuelan opposition leader, Juan Guaido, swore himself in as interim head of state on Wednesday, with the support of the United States and many Latin American nations, leaving Venezuela with two presidents.
Hundreds of thousands of anti-government protesters marched in Venezuela this week to demand the end of socialist President Nicolas Maduro's government.
The escalating political turmoil has seen a spike in the number of Venezuelans crossing over the Simon Bolivar pedestrian bridge into Colombia's border city of Cucuta.
Every day, 35,000 to 40,000 Venezuelans had been crossing the bridge into Colombia, many to buy food and medicine unavailable in Venezuela. Typically, 5,000 of those planned to stay in Colombia or in other South American countries.
"The numbers are up. You are now talking about 42,000 to 46,000 a day. We have seen growing numbers of people coming in daily and coming in to stock up on food," said Marianne Menjivar, Colombia country director at the aid group International Rescue Committee.
"The issue in Venezuela right now is that these organised protests and the political situation is a lot more unstable, and people don't know what's going to happen and that creates uncertainty," she told the Thomson Reuters Foundation.
Too poor to afford a plane or bus ticket, growing numbers of Venezuelans, some carrying babies in their arms and pushing prams, are on foot.
"We're also seeing a massive surge of walkers," Ms Menjivar said. "Those people aren't going back. They're walking their way across Colombia and heading to other countries in the region."
One migrant shelter in northern Colombia has seen the number of Venezuelans arriving increase from 700 people a week to 5,000 in the past week alone, Ms Menjivar said.
Unknown numbers of migrants are also crossing into Colombia using informal and hidden footpaths.
"What we are seeing is the tip of the iceberg," said Jemilah Mahmood, undersecretary-general for partnerships at the International Federation of Red Cross and Red Crescent Societies.
Providing shelter and healthcare, including first aid, for migrants are key priorities, as is psychological support.
"I think the psychological impact of this situation cannot be underestimated," said Ms Mahmood, a doctor.
"The pressures, not just on women and children, but on young men who are supposed to be breadwinners ... feeling very helpless."
Food shortages and record hyperinflation in Venezuela have put buying food out of reach for many. This, in turn, means migrants crossing the border are more malnourished and sick.
"The greatest humanitarian needs are still people coming increasingly with less and less body weight, in a worse nutritional state," Ms Menjivar said.
"Right now there is no cancer treatment in Venezuela, there's no treatment for HIV positive people, there's no treatment for diabetics .. so people are coming out sick."
Self-declared interim president Guaido has promised that humanitarian aid would be distributed with the oversight of congress.
With the highest number of Venezuelans living in Colombia - more than 1 million - its schools, hospitals and other services are struggling to cope.
The main public hospital in Cucuta says its maternity ward is overwhelmed with pregnant Venezuelan women giving birth, and that it can only provide emergency healthcare.
Schools in Cucuta and Bogota are also struggling to take in all migrant children who apply, and many are left with no school to go to.
About 3.3 million people have fled Venezuela since 2015 and the United Nations estimates about two million more, from a population of 32 million, could follow this year.
"This was a crisis that was unforeseen, unplanned and is overwhelming. The magnitude is huge, the rate of change is so fast that nobody can keep up," Ms Menjivar said.