By Agence France-Presse
Socialist leader Nicolas Maduro has vowed not to allow in the aid, which he's dismissed as a show and pretext for a US invasion.
On the eve of the face-off Guaido defied a government ban on leaving the country and attended a concert organized by British billionaire entrepreneur Richard Branson just over the border in Colombia. The concert is aimed at raising funds to help the relief effort.
Guaido sensationally claimed that the Venezuelan military, whose high command has repeatedly declared absolute loyalty to Maduro, "participated in this process" to get him into Colombia.
Hours later, Caracas said it had sealed the Colombian border across the whole of Tachira -- the western state that borders Cucuta -- citing threats to Venezuela's security.
On Saturday "the whole of Venezuela will be in the streets demanding the entry of the humanitarian aid," said Guaido.
Venezuela is gripped by a humanitarian crisis that has seen poverty soar during four years of recession leaving shortages of basic necessities such as food and medicine.
Guaido announced earlier that February 23 would be the day aid would come in, regardless of a military blockade.
The 35-year-old leader of Venezuela's National Assembly declared himself interim president exactly one month ago Saturday and is calling for fresh polls, branding Maduro a "usurper" and accusing him of rigging his re-election last May.
Humanitarian aid has become the key focus of the stand-off between Maduro and Guaido.
With the main crossing bridge on the Colombian border barricaded by Venezuela's military, it was not clear how Guaido would achieve his aim, although he had said he wanted to mobilize one million people to help him.
On Friday the tense aid stand-off turned deadly when two people were killed and 15 wounded as they tried to prevent Venezuelan troops from blocking an entry point on the Brazilian border.
That led UN Secretary-General Antonio Guterres to urge authorities not to use lethal force against protesters.
"An indigenous woman and her husband were killed and at least 15 other members of the Pemon indigenous community were injured," said a local human rights group, Kape Kape.
The clash occurred in southeastern Bolivar state close to the border with Brazil, which Maduro ordered closed on Thursday.
Guaido called on the military to arrest those responsible for the killings, "or you will be responsible."
"It wasn't a clash, it was an attack," said Salomon Perez, who accompanied a brother and two nieces suffering from gunshot wounds by ambulance to a hospital in Brazil.
The White House said the United States "strongly condemns the Venezuelan military's use of force against unarmed civilians and innocent volunteers" on the border with Brazil. "The world is watching," the statement added.
Guaido boosted his supporters on Friday by attending the "Venezuela Live Aid" concert organized by Branson in support of the opposition leader's humanitarian aid relief plan.
Guaido joined Colombian President Ivan Duque, Chile's Sebastian Pinera and Mario Abdo of Paraguay in saluting the crowd before the concert ended.
As many as 300,000 Venezuelans are in dire need of food and medicine after years of shortages and malnutrition, according to Guaido.
Some 2.7 million people have fled Venezuela since 2015 amid a devastating political and economic crisis, according to UN figures released Friday.
The UN said people were fleeing the crisis at a rate of 5,000 a day.
'Very bad situation'
Maduro, who has support from China, Russia and the military high command, has blocked the entry of aid and accused the United States of plotting a military intervention.
US special representative Elliott Abrams kept up the foreign pressure on Maduro on Friday, joining a Cucuta-bound plane carrying medical supplies and food.
Moscow has blasted Washington for using aid as a "convenient pretext for conducting military action."
Government supporters and opponents are expected in the streets of Caracas on Saturday.
"We must break the impasse, end the humanitarian crisis," Branson told the crowd shortly before the concert, which featured some of the biggest names in Spanish-language music.
Branson said he hopes to raise $100 million for humanitarian aid over the next 60 days via internet donations. Meanwhile aid is being stockpiled in Colombia, Brazil and the Caribbean island of Curacao because of Maduro's ban.
The concert was broadcast live online, and featured tickers showing people how to donate money.
Maduro's rival concert, decidedly smaller and featuring Venezuelan and Cuban artists, began hours later nearby on the Venezuelan side of the border in Urena.
Performers took to the stage against a giant backdrop emblazoned with the words "#Trump Hands off Venezuela," with around 2,500 people in attendance.
"We don't want to be interfered with, we don't want to be invaded," said Johana Suarez.
Maduro, who was not seen at the concert, said the event would last until Sunday.