People in the US are still waiting to learn the final outcome of Tuesday's midterm elections, three days into vote counting.

US media outlets predict Republicans will take a majority in the House, but the gap with President Joe Biden's Democrats will be narrow.

ABC News has projected the Democratic Party will win 48 of the Senate's 100 seats, with the Republican Party to secure 49.

The Associated Press is reporting that three states have yet to release their Senate results.

Ballot counting is ongoing in the two western states of Arizona and Nevada, with the counting of mail-in votes yet to be completed.

In Arizona, with about 78 percent of votes counted, the incumbent Democratic candidate was on 51 percent with the challenger Republican on 46 percent.

In Nevada, the incumbent Democrat had reached 48 percent while the Republican candidate was on 49 percent. An estimated 90 percent of votes have been counted.

The state of Georgia, where neither side achieved the required majority, will hold a runoff election in December.

The AP is reporting that Republicans are certain to win 211 seats in the House of Representatives, while Democrats have secured 194.

But neither party is yet certain to win the 218 seats needed to control the 435-seat lower chamber.

The Washington Post says the Republican Party is likely to win about 220 seats, delivering a House majority, although the gap is smaller than initially predicted.

It says results will still take time as the races remain tight in many places.