Venezuela's President Nicolás Maduro has closed the border with Brazil amid a row over humanitarian aid.
The embattled leader said he could also shut the key border with Colombia to stop the opposition bringing in relief.
He denies any crisis and calls the aid delivery plans a US-orchestrated show. His ally Russia has accused the US of trying to arm Venezuela's opposition.
Rival concerts will be held on both sides of a bridge linking Venezuela and Colombia later on Friday.
On the Colombian side, an event will be held to raise money for Venezuela. At the same time, Mr Maduro's government will hold its own concert, just 300m (980ft) away.
Opposition leader Juan Guaidó and his allies hope to collect food and medicine being gathered in neighbouring Brazil and Colombia on Saturday, in defiance of President Maduro.
Head of the National Assembly, Mr Guaidó declared himself interim leader during anti-government protests last month and is recognised by dozens of countries, including the US and most Latin American nations.
The border crossing with Brazil remained closed on Friday morning but local G1 website reported that a group of Venezuelans managed to cross from the Brazilian city of Pacaraima on foot using an unofficial route.
Mr Maduro announced on Thursday that the border would be closed "completely and absolutely" until further notice and said he had been considering a "total closure" of the border with Colombia.
Brazil had earlier said that, in co-ordination with the US, food and medicine would be available to be collected by "the government of acting President Juan Guaidó in Venezuelan trucks driven by Venezuelans".