At least two people have been killed after clashes with security forces in the Venezuelan town of Santa Elene de Uairen.
They had clashed with security forces over the opposition's plan to bring in aid from nearby Brazil.
President Maduro deployed troops and armoured vehicles to turn back humanitarian assistance at border crossings with Colombia and Brazil.
At the Colombian border town of Cucuta, Venezuela's National Guard were seen firing tear gas at protesters.
The protesters, some of them masked youth throwing rocks who demanded that humanitarian aid pass through.
Opposition leader Juan Guaido gave a personal send-off on Saturday to a convoy carrying US aid departing from Cucuta.
The convoy is hoping to transport nearly 200 metric tons of mostly US-supplied emergency food and medical supplies.
"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.
In response, president Maduro said he was breaking diplomatic relations with Colombia and ordered its diplomatic staff to leave Venezuela within 24 hours.
He claimed it was because of Colombia's assistance to opposition leader Juan Guaido.
Earlier today, three members of Venezuela’s National Guard deserted their posts and solicited help from Colombia.
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.
Additional reporting by agencies.
