Venezuela’s National Guard fired tear gas on residents clearing a barricaded border bridge to Colombia on Saturday, as the opposition began making good on its high-risk plan to deliver humanitarian aid despite objections from President Nicolas Maduro.

By midday, opposition leader Juan Guaido pulled himself on to a truck and shook hands with its driver as he and Colombian President Ivan Duque gave a ceremonial send off to an aid convoy.

The convoy wants to transport nearly 200 metric tons of mostly US-supplied emergency food and medical supplies from the Colombian city of Cucuta.

“Our call to the armed forces couldn’t be clearer: put yourself on the right side of history,” said Guaido, in an appeal to troops who constitute Maduro’s last-remaining major plank of support in a country ravaged by hyperinflation and widespread shortages.

The opposition is calling on masses of Venezuelans to form a “humanitarian avalanche” to escort trucks carrying the aid across several border bridges.

Venezuelan officials had ordered the border with Colombia closed after already shutting down crossings from Brazil and the island of Curacao, other points of entry for the aid.

But the residents in Urena defied government orders and began removing yellow metal barricades and barbed wire.

Later, three members of Venezuela’s National Guard deserted their posts and solicited help from Colombia.

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Venezuelans ride on semi-trailers to the Simon Bolivar international bridge, accompanying humanitarian aid destined for Venezuela (Fernando Vergara/AP)

Colombian migration authorities said they received the request early on Saturday at the Simon Bolivar bridge connecting the two countries.

There was no immediate word on the guardsmen’s rank. But a video provided by Colombian authorities show the men wading through a crowd with their assault rifles and pistols held above their heads in a sign of surrender.

The young soldiers were then ordered to lay face down on the ground as migration officials urged onlookers to keep a safe distance.

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Humanitarian aid bound for Venezuela (Fernando Vergara/AP)

Meanwhile thousands of people flooded the streets of Venezuela’s capital in rival demonstrations.

In Caracas, Maduro loyalists marched to the city centre to the sounds of brass bands, while others rode motorbikes.

Opposition supporters converged on a Caracas military base, urging soldiers to join their fight.

Many were dressed in the colours of Venezuela’s flag and some in costume as Captain America characters.