Pope Francis has visited Mexico's gang-infested heartland, calling on priests to combat the scourges of corruption and drug trafficking that have stoked a decade of blood-letting that the government has been unable to stop.

Gang wars over the lucrative methamphetamine trade have torn the western state of Michoacan apart, while widespread kidnapping and extortion by gangs have sparked an uprising by vigilante groups.

The Pope on Tuesday (local time) visited Morelia, Michoacan's picturesque capital known for its Spanish colonial architecture, amid tight security given scattered outbursts of violence in recent months.

"What temptation can come to us from places often dominated by violence, corruption, drug trafficking, disregard for human dignity, and indifference in the face of suffering and vulnerability?" the Pope asked an estimated 30,000 priests, nuns and seminarians at a Mass in a Morelia stadium.

Tens of thousands more people lined the streets outside for a glimpse of the first Latin American pontiff, who is travelling to some of the poorest and most violent corners of the country on his six-day trip to Mexico.

The Argentine pontiff urged priests not to be resigned to evils around them like drug trafficking, and not to remain entrenched in their churches, but rather to head out to the front lines to help those suffering.

Before the Pope entered, the crowd in the stadium counted aloud to 43, a gesture to remember dozens of trainee teachers who were abducted and apparently massacred by a drug gang in league with corrupt police in 2014 in the neighbouring state of Guerrero.

Relatives of the students have lobbied for a meeting with the Pope, but his spokesman has said some of them will be at a mass on Wednesday when the Pope visits Ciudad Juarez on the US border, once one of the world's deadliest cities.

"It's a miracle that he has chosen to come here to lift our spirits," said housewife Maria Hernandez, 66. "Michoacan has suffered so much."

In his first trip to Mexico as pontiff, Francis has had some sharp words for a privileged elite that he accused of exploiting the nation's poor.

In Mexico City, he chastised bishops for being gossips obsessed with coddling wealthy patrons and failing to denounce the evils of the drug trade.

Francis is set to visit Morelia's downtown cathedral on Tuesday and meet with youth groups.

"Everyone is hoping he brings some comfort, something that makes the people react and see things differently," said Miguel Angel Ruiz, a 58-year-old industrial consultant.

In early 2014, Michoacan descended into bitter conflict as vigilante groups took up arms against the powerful Knights Templar drug gang.

President Enrique Pena Nieto's government later sent in the army and forged an uneasy alliance with the vigilantes, offering them jobs in the police force, but progress was muted.

More than 100,000 people have been killed in Mexico's drug war over the last decade.

Reuters