Tens of thousands of protesters poured into the streets of Caracas on Saturday in rival displays for and against embattled Venezuelan President Nicolas Maduro, as an air force general became the highest-ranking officer to recognise opposition leader Juan Guaido as the crisis-torn country's acting president.

The rival rallies, convened in different parts of the city, come on the eve of a deadline set by the EU and other European powers for Maduro to call “free elections” or have them recognise Guaido.

Guaido has promised a huge turnout — the largest in the country's history, he has said — to reinforce his call for elections organised by a transitional government he claims to lead as head of the National Assembly.

Carrying Venezuelan flags and blowing horns and whistles, his supporters began massing at five locations around the city for a march on EU headquarters in eastern Caracas.

The pro-Maduro forces were rallying in the western side of the city to mark the 20th anniversary of the rise of power of the late Hugo Chavez, the leftist firebrand who installed a socialist government.

Hundreds of members of a civilian militia, public workers and people who have benefitted from the government's social programmes began to concentrate in the downtown Avenida Bolivar in a show of support for their beleaguered leader.

Maduro has proposed holding early elections for the National Assembly as he seeks to outmanoeuvre a renewed opposition that is trying to use its control of the legislature to challenge his rule.

Maduro in a speech to supporters on Saturday said it would be up to the pro-government constitutional assembly to decide whether or not to back his proposal.

Elections for the opposition-controlled National Assembly aren't supposed to take place again until 2020.

International pressure

The challenge to Maduro, Chavez's handpicked successor, is his most serious yet, with the United States, Canada and nearly a dozen Latin American countries piling on pressure for his removal from office.

“Maduro's tyranny must end and must end now,” US Vice President Mike Pence told a rally of exiled Venezuelans in Miami on Friday.

Underscoring the high stakes, Air Force Major General Francisco Yanez announced in a video posted on social media that he disavowed Maduro's “dictatorial” authority and recognised Guaido as the acting president.

Yanez, the strategic planning director of the air force high command, commands no troops but he was the highest ranking active duty officer to defect — “a hard blow” to the military leadership, which has pledged absolute loyalty to Maduro, said Rocio San Miguel, an expert on the Venezuelan military.

The military and security forces have so far been Maduro's main pillar of support, despite an economic collapse that has created dire shortages of food and medicine and a mass migration to neighboring countries.

But there have been signs of unrest in the ranks.

Take a look: Venezuela turmoil

On January 21, a group of National Guard soldiers rose up against Maduro in Caracas.

The mutiny was quickly put down and 27 soldiers were arrested, but it kicked off a week of violent street clashes between civilians and security forces that the UN said left 40 dead and 850 arrested.

Speaking from an unknown location, Yanez said “90 per cent of the armed forces don't support the dictator, they're with the Venezuelan people.”

Guaido, who has offered amnesty to members of the military that abandon Maduro, acknowledges that he needs its support.

This week he claimed to have held “clandestine meetings with members of the armed forces and the security forces.”

Assurances to China

Guaido, 35, also moved to reassure China — Venezuela's main creditor and a long-time ally of the socialist regime — that he would honor bilateral agreements if successful in ousting Maduro.

China has denounced outside interference in Venezuela but — unlike Russia, another major creditor that has backed Maduro — so far has declined to pick sides.

Guaido told the South China Morning Post he would not disrupt the relationship with China despite his close ties to Washington.

“China's support will be very important in boosting our country's economy and future development,” he said in an email interview.

“We are ready to begin a constructive relationship and dialogue with China as soon as possible.”

China's foreign ministry spokesman Geng Shuang said cooperation between the countries would continue “no matter how the situation changes” in Venezuela.

European Parliament lawmakers recognised Guaido on Thursday as the interim head of state.

And four major European powers — Britain, France, Germany and Spain — have said they will do so if Maduro fails to call presidential elections by midnight on Sunday.

The international heave against Maduro's leftist regime came after weeks of behind-the-scenes diplomacy including secret talks in Washington between Guaido and US officials.

'Time for action'

“Let me be very clear: this is no time for dialogue. This is time for action,” Pence warned on Friday. “The time has come to end Maduro's dictatorship once and for all.”

In a letter to the presidents of Mexico and Uruguay published on Friday, Guaido ruled out any negotiations with Maduro unless they “start the transition process, culminating in the holding of free elections”.