Meanwhile Obama was predicted to win his home state of Illinois
and scored a convincing victory in Georgia
In the Republican, race McCain was predicted to dominate the results in the east of the country winning New York
, New Jersey
The former Arizona
senator was looking to deliver a knock out blow to his nearest rival Mitt Romney.
Although trailing in polls, Romney had maintained he could make a comeback but was losing key southern states to Mike Huckabee, who was predicted to do far better than expected.
Romney had hoped to do well in the south but projections showed Huckabee, a former Baptist minister and governor of Arkansas
, on course for victory in Alabama
, West Virginia
Al Jazeera's James Bays
in New York
said that a key factor why McCain was projected as doing well in New Jersey
is Rudy Giuliani, the former mayor of New York
Giuliani was the leading candidate in the region and has pledged his support to McCain after he withdrew from the race and that could be why McCain is doing so well, Bays explained.Democratic prospects
In the Democratic race, Obama had been expected to win in the southern state of Georgia.
The Democrats have strong prospects of winning the White House in November, given the weak US
economy, the ongoing bloodshed in Iraq
and the low popularity of George Bush, the current Republican president.
The Democratic contest has turned into a historic race between Clinton, who is trying to become the first woman to win the White House, and Obama, seeking to become the first black US president.
The two split the early primaries and caucuses. But few delegates were at stake in those contests, which were mostly about building momentum and establishing front-runners.
A total of 1,681 delegates are at stake for Obama and Clinton in Tuesday's races, and 2,025 delegates are needed to win the Democratic nomination.
Clinton voted in suburban New York, accompanied by her husband, former president Bill Clinton. Obama headed back to Illinois after a round of television and radio interviews.
Given his huge lead in polls, McCain could effectively wrap up the nomination on Tuesday, a remarkable comeback for a candidate whose hopes appeared dashed last year.
McCain could be the most formidable opponent for Clinton or Obama because he draws support from independent voters.
He had commanding double-digit leads in many of the largest states.
"We're going to win today, we're going to win the nomination and we're going to win the presidency," McCain told a crowd of several hundred at an early morning rally at New York's Rockefeller Centre.
A total of 24 US states are holding primaries or caucuses on Feb 5
It is the day when the largest number of nominating delegates for both Republicans and Democrats are up for grabs
52 per cent of Democratic delegates and 41 per cent of Republican delegates are at stake
Key states include California - with the most amount of delegates for a single state - Georgia, Illinois and New York
Started in 1988 after some southern US states decided to hold primaries simultaenously to boost southern influence in choosing a candidate
Yet many Republicans remain wary of McCain, questioning the senator's conservative credentials because of his reputation as a maverick and his stance backing a path to citizenship for illegal immigrants.
Romney has tried, so far unsuccessfully, to tap into those doubts.
"We're going to hand the liberals in our party a little surprise," boasted Romney, the former Massachusetts governor, predicting he would score an upset in California, which has 170 delegates.
In the Republican race, there are 1,023 delegates at stake in primaries in 15 states, caucuses in five and the West Virginia state convention.
A candidate needs 1,191 delegates to secure the nomination
California will be one of the last states to declare its results in both races and holds the largest number of delegates.
Source: Al Jazeera and agencies