The demonstrators, who included teachers and healthcare workers, gathered at the entrance of a military barracks in Chiapas state where Lopez Obrador had planned to hold a cabinet meeting and press conference.
The president said in a video message recorded from inside his vehicle that the protesters were refusing to let him pass until he answered their demands.
“I cannot allow this because the president cannot be held hostage by anyone,” he said.
Demonstrators shouted anti-government slogans and scrawled the initials of their teachers’ union on his vehicle with marker pens.
Television images showed Lopez Obrador lowering the window of the vehicle and telling one of the protesters: “I don’t accept blackmail ... respect me and then we talk.”
Mexican teachers often strike, and Lopez Obrador has previously praised powerful teaching unions that have in the past protested, sometimes violently, against centrist and right-wing Mexican governments.
The latest protests were related to the most recent teaching reforms, Mexican newspapers said.
Since assuming office in December 2018, Lopez Obrador has used his morning news conferences – which begin at 7am and can last over two hours – to set the political agenda and take critics to task.
By midmorning, la mañanera, as the morning news conference is colloquially known, was trending on Twitter in Mexico.
Most of the morning news conferences take place in Mexico City, but he sometimes conducts them while travelling around the country.
“They have a right to protest. We will respect that,” Lopez Obrador said, in reference to the teachers, his video message transmitted on a screen in the background of an empty lectern and the Mexican flag. “We are offering them dialogue.”
Eventually the protesters dispersed and allowed the convoy through.
