Former Massachusetts Gov. Mitt Romney has won the Arizona primary, according to multiple projections, but the crucial state of Michigan remains too close to call.

The Arizona win was a boost for the beleaguered Romney presidential campaign, helping him pick up much-needed delegates to secure the Republican nomination. The state may also be a battleground in the November elections.

But all eyes were on Michigan, where Romney grew up and where his father was a popular governor.

Early returns from that state showed Romney running neck and neck with former Pennsylvania Sen. Rick Santorum (Pa.).

Rep. Ron Paul (Texas) and former Speaker Newt Gingrich (Ga.) trailed Romney and Santorum in both states.

Speaking before the polls closed, Gingrich said he would focus on Super Tuesday contests in 10 states, including Georgia, and made no reference to Arizona or Michigan.