A Utah man imprisoned in Venezuela for two years without trial has made an emotional plea for help, saying in clandestinely shot videos that a prison riot is underway and his life is at risk.

In two 20-second videos filmed on a mobile phone and posted on his Facebook page today, a visibly distraught Joshua Holt suggested his patience was running out with the US Government, which has made his release a top priority in its dealings with Venezuela's socialist Government.

"I've been begging my Government for two years. They say they're doing things, but I'm still here," Holt said.

The 26-year-old travelled to Venezuela in 2016 to marry a fellow Mormon he met on the internet.

Shortly afterward, the couple was arrested at her family's apartment in a Caracas public housing project after police said they found him stockpiling arms — an assault weapon and grenades.

"Please my fellow Americans don't allow me to continue suffering in Venezuela," Mr Holt said in a written message, also posted on his Facebook page.

"I am not a political pawn, I am a human being, a child of God and I just want to live happy with my wife and children. I have NEVER done anything wrong in my life. Please help me!"

His first-ever video message from jail came amid what the US Government described as a riot by fellow inmates, including some of President Nicolas Maduro's top opponents who are being held alongside the American.

The disturbance, the extent of which was not immediately known, has come days before a presidential election which has Venezuelans on edge.

Mr Maduro is widely expected to win despite a crushing economic crisis marked by widespread shortages and hyperinflation.

"The people have taken the entire prison," Mr Holt said in one of the videos.

"They're trying to break in. They're saying they want to kill me. They're saying they want me as their guarantee."

Chief prosecutor Tarek William Saab said he sent a delegation to the prison to speak with a representative of the inmates.

While he did not provide details about the disturbance, or what sparked it, he said the delegates offered to coordinate with prison and judicial authorities to address the inmates' demands.

US warns Venezuela to ensure Holt's safety

The Trump administration has suggested there are political motives for Mr Holt's continued detention.

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His trial on weapons charges was scheduled to start on Tuesday but Mr Holt and his wife, Thamara Caleno, were not taken to the court house by their jailers at El Helicoide, headquarters to Venezuela's feared Sebin intelligence police.

"The Sebin has told me that as long as my Government continues attacking this Government, and as long as Marco Rubio continues talking about me, the longer that they will never let me go," Mr Holt said in a written message, referring to the Republican senator from Florida who has accused Mr Maduro of keeping Mr Holt as a "hostage" to extract concessions from the US.

The Trump administration has warned it could put crippling oil sanctions on Venezuela if Mr Maduro goes ahead with what the US and others consider a sham presidential election on Sunday.

Several of Mr Maduro's top opponents are barred from running.

A group of about 30 people, many of them family members of inmates considered by many to be political prisoners, gathered outside the jail to seek information about their loved ones as a number of videos and audio recordings from inside the jail flooded social media.

None of the prisoners' claims could be verified by The Associated Press.

In one video, Daniel Ceballos, a former opposition mayor, is seen trying to jimmy open the padlock on a cell using a dumbbell and iron rod.

In another, a shirtless youth runs down a narrow hallway and knocks out an overhead light with a long stick to shouts of encouragement by other inmates.

The US embassy released a photo of Todd Robinson, the top American diplomat in Venezuela, leaving the foreign ministry and saying he had received no information from the Government about the "riot".

"We are concerned about the riot at El Helicoide," Mr Robinson said in a statement, referring to the helix-shaped building where Maduro's top opponents are being held.

"Joshua Holt and other US citizens are in danger.

"The Government of Venezuela is directly responsible for their safety and will be held responsible if anything happens to them.

"We renew our call for the Government to release Joshua Holt on humanitarian grounds."

AP