President Nicolas Maduro ordered the closure of Venezuela's border with Brazil on Thursday in an increasingly fraught power struggle. Guaido set out in a convoy of vehicles to personally pick up US aid being stockpiled on the other side of the Colombian border, defying Maduro's military to stop him.
Recognized as interim president by more than 50 countries, he left the capital Caracas for the Colombian border in a convoy of several vehicles for the 900-kilometre trip.
Embattled Maduro has dismissed Guaido's humanitarian caravan as a cheap show and slammed aid as a precursor for a US military intervention in the oil-rich but crippled Latin American country.
The 35-year-old leader of the Venezuelan legislature proclaimed himself acting president Jan 23 and wants to oust Maduro, set up a transitional government and hold new elections.
A separate caravan of buses and trucks containing opposition lawmakers had earlier left eastern Caracas bound for the border.
Several of the trucks were stopped by security forces and their drivers forced to get out, but the rest of the caravan was allowed to continue, lawmakers said.
We know that the regime is going to put all obstacles to prevent us from reaching the border, but nothing is stopping us, we are going to continue, said opposition lawmaker Yanet Fermin.
Signaling his growing disquiet, Maduro announced on Thursday that the border with Brazil - which along with Colombia is one of the main potential avenues for aid delivery would be completely and absolutely closed from 8:00 pm until further notice.
Maria Teresa Belandria, Guaido's designated ambassador in Brazil, said aid deliveries would go ahead nonetheless. The operation goes on. There's no going back.
She said 100 tons of food, medicines and emergency kits were waiting to be trucked from Boa Vista to Pacaraima on the Venezuelan border.
Maduro also warned on Thursday he was considering a total closure of the border with Colombia to Venezuela's west.
He has already ordered the military to barricade a major border bridge to prevent supplies from entering the country from Cucuta, Colombia, where tons of humanitarian aid are being stockpiled, most of it from the United States.
The military announced a ban on vessels putting to sea from Venezuelan ports until Sunday to avoid actions by criminal groups.
Meanwhile, Maduro - mirroring Guaido's move in an attempt to show his socialist government was able to look after its people - ordered a shipment of thousands of food boxes to be distributed to the needy along the Colombian border.
Shipments of food and medicine for the crisis-stricken population have become a key focus of the power struggle between Maduro and Guaido.
Guaido, who says 300,000 people could die without an influx of aid, says he aims to rally a million volunteers to start bringing it in by Saturday.
It remained unclear how he proposed to do so if the blockade continues, but experts have pointed to the notoriously porous 2,200 kilometre border, which is perforated by well-worn drug trafficking and contraband routes.
Guaido said the planned entry points for aid were the Brazilian and Colombian borders, the island of Curacao and the seaports of Puerto Cabello and La Guaira.
Venezuela's vice-president Delcy Rodriguez said the government was shutting down air and sea links between Curacao and Venezuela.
However Carlos Faria, one of the leaders of a group of Venezuelans organizing aid shipments via Curacao, revealed a plane carrying 50 tons of food and medicine was expected from Miami on Thursday and would be loaded onto a Venezuela-bound ship on Friday.
Amnesty International's Americas director Erika Guevara urged authorities to guarantee access for those bringing in aid.