A restaurant in Dearborn, Michigan, shows a telecast of on the Michigan primary election on Tuesday. AFP

Joe Biden scored an easy win in Michigan's presidential primary on Tuesday but was dealt a stinging rebuke over the war in Gaza in an Arab American-led protest that raised concerns over his bid to win the swing state in November's election.

There was little suspense over the outcome for both parties, with the president almost unopposed in the Democratic nominating contest and his predecessor Donald Trump declared the victor in the Republican vote as polls were closing.

But tens of thousands of Democrats in a swing state crucial to Biden's reelection hopes ticked the "uncommitted" box as part of a push by the "Listen to Michigan" campaign to jolt the president into backing off from his support of Israel.

With almost two-thirds of polling stations still to report, the "uncommitted" share accounted for 50,000 votes, more than double the final totals in each of the last three election cycles.

Biden released a statement thanking voters, touting his record on working for Michigan's middle class and acknowledging that there was "much left to do" -- but made no mention of the Gaza conflict and ignored the protest vote.

Mayor of Dearborn, Michigan delivers remarks at an "Uncommitted for Joe Biden" primary election night. AFP

"Listen to Michigan" had set a modest goal of rallying 10,000 uncommitted voters in its aim to censure the president over US military funding for Israel, and to pressure him to call for an immediate ceasefire.

"President Biden has funded the bombs falling on the family members of people who live right here in Michigan -- people who voted for him, who now feel completely betrayed," the campaign said in a statement claiming victory.

'Completely betrayed'

The Gaza war started when Hamas attacked Israel on October 7, resulting in the deaths of about 1,160 people in Israel, mostly civilians, according to an AFP tally of official Israeli figures.

But concern has mounted amid the high civilian death toll in Israel's retaliatory campaign, now at almost 30,000, according to the health ministry in Hamas-run Gaza.

The bloodshed has weakened Biden's standing among Muslims and Arab Americans, a bloc crucial to his 2020 victory in Michigan over Trump.

The Midwestern state has the largest proportion of residents who identify as being of Middle Eastern or North African descent in the country, with most of the population concentrated around Detroit.

The protest never threatened Biden's easy march to the nomination, and his sole challenger, Minnesota congressman Dean Phillips, was trailing with under three percent support late Tuesday.

Agence France-Presse