Bernie Sanders speaks at a rally at Bonanza High School in Las Vegas on Sunday. (Photo by Ethan Miller/Getty Images)

YPSILANTI, Mich. -- Democratic presidential hopeful Bernie Sanders met Monday with a small group of residents affected by the contaminated water crisis in Flint, Mich., before addressing a basketball arena filled with an estimated 9,400 supporters here.

The senator from Vermont said his private meeting with seven or eight Flint residents was among the most difficult in his public life, and he confessed that he had not realized “how ugly and how horrible and how terrible” the situation is.

“It is beyond my comprehension in the year 2016 in the United States of America we are poisoning our children,” Sanders told the crowd here at Eastern Michigan University after meeting with Flint residents.

Sanders said one of the women he met with was a mother who has seen her child’s schoolwork deteriorate.

“Can you imagine being a mother, seeing your own baby’s, your own child’s intellectual development deteriorate in front of your very eyes?” Sanders asked.

His Democratic rival, Hillary Clinton, has made her advocacy for Flint residents a focal point of her campaign in recent weeks.

The former secretary of state released a new campaign video Monday that features residents of the majority African American city talking about how the poisoned water makes it hard to drink and bathe. Clinton also announced endorsements Monday from three ministers from the city, where a cost-saving decision to switch the water supply resulted in contamination from lead and other sources.

Sanders has called for the resignation of Michigan Gov. Rick Snyder (R) in connection with the crisis but has otherwise taken a lower-key approach. The Vermont senator’s meeting with the Flint residents was closed to the media, aides said, because Sanders did not want to exploit the situation.

Michigan's Democratic primary is March 8.

Addressing a crowd dominated by students in the basketball arena, Sanders spoke for more than an hour about his agenda to confront the “billionaire class” and advance an array of initiatives to help working families.

“The American people are sick and tired of massive and grotesque levels of income and wealth inequality,” Sanders said.

The boisterous crowd interrupted him frequently with applause and chants of “Bernie! Bernie! Bernie!”

During his campaign swing in Michigan, Sanders also planned Monday to address an evening rally of auto workers.