Venezuelan President Nicolás Maduro has announced the closure of the border with Brazil as a row over foreign humanitarian aid continues.
The embattled leftist leader went on TV to say that he was also considering shutting the border with Colombia to stop the opposition bringing in relief.
He denies any crisis and calls the aid delivery plans a US-orchestrated show.
Opposition leader Juan Guaidó is leading a convoy from the capital, Caracas, to the Colombian border.
Later on Friday, a huge concert will be held on the Colombian side of the border to raise money for Venezuela.
At the same time, Mr Maduro’s government will hold its own event, reportedly just some 300 metres away.
Mr Guaidó declared himself interim leader during anti-government protests last month and is recognised by dozens of foreign states, including the US and most Latin American countries.
Scuffles broke out and tear gas was fired when the convoy of buses and cars was briefly stopped by security forces on a road near Mariara, west of Caracas, but they later moved on.
Meanwhile, after Mr Maduro’s announcement that the border would be closed indefinitely on Thursday night, many Venezuelans rushed across the frontier to the Brazilian city of Pacaraima to stock up on supplies, Brazilian news portal G1 reported.
The crossing usually closes at night and would normally have opened at 08:00 local time (12:00 GMT) on Friday.
Mr Guaidó and his allies hope to collect food and medicine in defiance of President Maduro.
The Venezuelan military has so far managed to block shipments of US aid from coming across the border with Colombia.
Despite denying there is any humanitarian crisis, Mr Maduro announced this week that 300 tonnes of aid would be shipped to Venezuela from its ally Russia.