Washington, Feb 6: Democrat Hillary Clinton traded key ''Super Tuesday'' victories with rival Barack Obama and Republican John McCain rolled to big wins in the US Northeast as 24 states voted in contests that could help pick the presidential nominees of both parties.

In their hard-fought duel for the Democratic nomination, Obama won seven states and Clinton six in the early returns.

Clinton won Oklahoma, Tennessee, Arkansas, Massachusetts, New Jersey and her home state of New York. Obama scored victories in Georgia, Delaware, Alabama, Kansas, North Dakota, Utah and his home state of Illinois.

McCain, hoping to knock rivals Mitt Romney and Mike Huckabee out of the race with a strong night, cruised to wins in Connecticut, New Jersey, Delaware, New York, Illinois and Oklahoma on the biggest day of US presidential voting ahead of November's election.

Huckabee, a Baptist preacher and former Arkansas governor, won in Alabama, Arkansas and West Virginia. Huckabee had aimed for a strong showing in the South with its concentration of evangelical Christians. Romney won in Massachusetts, where he served as governor, and in Utah, where he ran the 2002 winter Olympics in Salt Lake City.

More than half the total delegates to the Democratic convention in August and about 40 per cent of the delegates to the Republican convention in September will be apportioned in yesterday's voting.

The delegates pick candidates for the November 4 election.

The split results, with all the contenders scoring at least one win, were likely to prolong the hard-fought nominating races in both parties. Another series of contests will take place in the coming week in a half-dozen states.

Economic worries -- plunging housing values, rising energy and food prices, jittery financial markets and new data showing a big contraction in the service sector -- eclipsed the Iraq war as voters' top concern, exit polls showed.