The contest is too close to call in the battlegrounds of Ohio, Pennsylvania, Virginia, Florida and North Carolina.
But Republican nominee Mr Trump racked up wins in the Midwest and South, while Democrat Mrs Clinton swept Northeastern states, ABC News projects.
Republicans are set to retain control in the House of Representatives.
As expected, Mr Trump has been victorious in the Republican strongholds of Alabama, Kentucky, South Carolina, Nebraska, Indiana, West Virginia, Mississippi, Tennessee, Oklahoma and Texas, ABC News projects.
He is also forecasted to win Missouri, Montana, Louisiana, Arkansas, Kansas, North Dakota, South Dakota and Wyoming - all solidly conservative states.
The network tips Mrs Clinton to have won the Democratic heartlands of New York, New Jersey, Connecticut, Massachusetts, Maryland, Vermont, Delaware, Illinois, Rhode Island, New Mexico and District of Columbia.
A candidate must secure 270 of the 538 electoral college votes to declare victory.
Voting has ended across more than two-thirds of the US, and full results are expected some time after 23:00 EST (04:00 GMT on Wednesday), once voting ends on the West Coast.