Vermont Sen. Bernie Sanders is opening up a sizable lead in the 2020 California Democratic presidential primary, two new polls show.

A UC Berkeley Institute of Governmental Studies poll of likely voters released Tuesday shows that Sanders is leading the field with 26 percent of survey respondents. He's followed by Massachusetts Sen. Elizabeth Warren at 20 percent and former Vice President Joe Biden at 15 percent. No other candidate reached double-digit support, with South Bend, Ind. Mayor Pete Buttigieg coming the closest at seven percent support.

Sanders has increased his lead in the time since the poll was conducted in late November, when he led the field with 24 percent support with Warren close behind at 22 percent. Biden was at 14 percent support the last time the poll was conducted, and Buttigieg was the only other candidate in double-digits at 12 percent. 2,895 likely voters participated in the poll, and the margin of error is at +/- 2.5 percent.

Additionally, a Change Research poll for KQED released Thursday shows Sanders with a commanding double-digit lead over both Biden and Warren. That poll shows Sanders at 30 percent support, followed by Warren 16 percent and Biden at 15 percent support. Like the UC Berkeley poll, the Change Research poll shows that no other candidate has double-digit support. The Change Research poll based on 1,967 interviews collected online and has a margin of error of +/- 3.4 percent.

UC Berkeley Institute of Governmental Studies poll director Mark DiCamillo noted that it's important to keep on eye on the 15 percent threshold as we get closer to the March 3 contest.

"Attaining the 15% threshold in the California primary is paramount, since the state’s delegates to the Democratic National Convention are awarded only to candidates who receive at least 15% of the vote either statewide or within the state’s fifty-three congressional district election," he wrote.

This could be a problem for former New York City Mayor Michael Bloomberg, who is focusing exclusively on Super Tuesday states such as California. He's spent millions of dollars on television ads in the state and was recently endorsed by San Francisco Mayor London Breed. He came in fifth place with six percent in the Berkeley poll, and seventh place with four percent in the Change Research poll.

You can check out the full poll results of the Berkeley poll here, and the full results of the Change Research poll here.

Eric Ting is an SFGATE digital reporter. Email: eric.ting@sfgate.com | Twitter:@_ericting