Venezuela's President Nicolas Maduro said he would shut the country's border with Brazil today "until further notice", amid a tense standoff with opposition leader Juan Guaido over allowing in humanitarian aid.

Maduro said the land border with Brazil would be "completely and absolutely" closed from 8pm (local time), following a meeting with the military high command.

The embattled socialist leader also said 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 tonnes of humanitarian aid are being stockpiled, most of it from the United States.

He said he was mulling the Colombia border closure following provocations from Colombian President Ivan Duque and US President Donald Trump.

"I hold Mr Ivan Duque personally responsible for any violence on the border," said Maduro after meeting his generals at their Fort Tiuna military headquarters in Caracas.

Guaido, recognised as the interim leader by 50 countries, was himself heading to the Colombian border today with his supporters to try to collect aid being stockpiled there.

The opposition leader said he has enlisted hundreds of thousands of volunteers to bring in aid in defiance of Maduro's blockade, claiming 300,000 people could perish if the blockade continues.

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Lawmakers scuffled with soldiers wearing riot gear on a roadblock at a tunnel some 100km along the main road between the countries, which forced several buses to stop.

Venezuelan opposition leader Juan Guaido left Caracas with some 80 lawmakers today, and headed for the Colombian border where they hope to receive humanitarian aid in defiance of President Nicolas Maduro, who threatened to close it.

Lawmakers said some vehicles managed to pass through the tunnel after being stuck for several hours but other buses remained behind.

Guaido's vehicle continued, lawmakers said, but his exact location was being kept a secret due to security concerns.

The Information Ministry did not respond to a request to comment.

Guaido is poised for a showdown with Maduro's beleaguered government on Saturday, when the opposition plans to attempt to bring in food and medicine piling up on the Colombian side.

Maduro denies there is a humanitarian crisis in Venezuela, and declared the Brazilian border closed. He also said he would close the Colombian border. The government has said soldiers will be stationed at crossing points to repel any "territorial violations."

The opposition lawmakers set off from Caracas just after 10am on a 800km road trip to the Colombian border.