A California gubernatorial debate was canceled just hours before it was set to occur on Tuesday after mounting criticism that only white candidates in the crowded field had qualified for the event.

The criteria to participate in the debate, which was set to be co-sponsored by the University of Southern California and the Los Angeles TV station KABC, had emerged in recent days as a source of controversy in the wide-open race to replace Gov. Gavin Newsom. The sprawling field includes eight prominent Democrats and two major Republicans, as well as several other lesser-known candidates.

USC had faced condemnation for using polling and fundraising criteria for participation in the debate that had resulted in the exclusion of all the nonwhite gubernatorial candidates.

In a statement from late Monday night, USC said that the “concerns about the selection criteria” for the debate had “created a significant distraction from the issues that matter to voters.”

“Unfortunately, USC and KABC have not been able to reach an agreement on expanding the number of candidates at tomorrow’s debate. As a result, USC has made the difficult decision to cancel tomorrow’s debate and will look for other opportunities to educate voters on the candidates and issues,” the university said in that statement.

The school added that it “vigorously defends the independence, objectivity, and integrity” of the formula it used to determine whether candidates qualified for the debate, saying it was “based on extensive research and enjoys broad academic support.”

KABC didn’t immediately respond to questions from NBC News about the canceled debate.

The lengthy list of Democrats running for governor in California includes Rep. Eric Swalwell; former Rep. Katie Porter; former Health and Human Services Secretary Xavier Becerra; former Los Angeles Mayor Antonio Villaraigosa, billionaire activist Tom Steyer; state Superintendent of Public Instruction Tony Thurmond; former state Controller Betty Yee and San Jose Mayor Matt Mahan.

At least 10 Republicans have also said they’re running, with Riverside County Sheriff Chad Bianco and former Fox News commentator Steve Hilton leading the pack.

In California, candidates from all parties appear on the same primary ballot, with the top two vote-getters advancing to the November election.

Much of the early polling ahead of the June 2 contest has shown there’s no clear front-runner. Some surveys have even put Republicans Bianco and Hilton among the candidates splitting the most support in a state that hasn’t elected a GOP governor in 20 years.

For Tuesday’s debate, USC and KABC had invited the five candidates who have largely been atop public polls in the race — Democrats Porter, Steyer and Swalwell and Republicans Bianco and Hilton — as well as Mahan to participate. Mahan trails other candidates in most of those surveys, but as the mayor of Silicon Valley’s hub city, he has quickly amassed a formidable financial war chest after jumping into the race late in January.

All six of those candidates are white. Those excluded from participation most notably were Becerra, Villaraigosa, Thurmond and Yee, none of whom is white.

The selection sparked growing anger from the campaigns of the excluded candidates, which culminated in a Friday evening news conference where they called on all invited participants to skip the debate.

“We ask each and every candidate who is in this race to recognize that if we can’t have a fair process for a debate, then we should all not participate,” Becerra said on Friday. “We call on them to withdraw from this biased forum.”

The Mahan and Steyer campaigns were working to still hold an event later Tuesday that would include the original list of participants, as well as those four excluded candidates, Mahan campaign spokesperson Tasha Dean told NBC News, but nothing had yet been finalized.

USC’s cancellation of the debate came amid fresh concerns from Democratic leaders in the state that the broad field of candidates could end up inadvertently hoisting a Republican into the governorship in the deep blue state.

In an open letter published this month, California Democratic Party Chair Rusty Hicks said the packed field could risk “locking out” any Democrat from the November ballot. He called on candidates who “do not have a viable path” to the general election to drop out of the race before April 15.