BOSTON -- Massachusetts voters are heading to the polls to choose the two candidates who will square off to fill the late Edward Kennedy's Senate seat.

Attorney General Martha Coakley, Rep. Michael Capuano, City Year service organization co-founder Alan Khazei and Boston Celtics co-owner Stephen Pagliuca are competing for the Democratic nomination. State Sen. Scott Brown and Duxbury businessman Jack E. Robinson are the candidates for the Republican nomination.

Coakley and Brown have led in public opinion polls.

The general election is Jan. 19.

Tuesday's primaries mark the first time since 1984 Massachusetts voters are casting ballots in a Senate race with no incumbent. Then they were filling the seat of Paul Tsongas after he stepped down because he had cancer.

Kennedy died of brain cancer in August at age 77.