WASHINGTON (BLOOMBERG) - The US election remains up in the air with the futures of Mr Donald Trump and Mr Joe Biden hinging on key battleground states that were too close to call and which may take until at least midday on Wednesday (Nov 4) to resolve.

With no "blue wave" for Democrats on Tuesday night, Mr Trump and Mr Biden are bracing themselves for a more drawn out process as ballots continued to be counted.

Early on Wednesday morning in the United States, Mr Biden won Arizona, flipping the first state to the Democrats compared with 2016, when Mr Trump beat Mrs Hillary Clinton.

Here's the state of play and when we might get clear results from the states set to determine this year's winner:

Pennsylvania

Pennsylvania was expected to be under scrutiny in a close race, with both campaigns aggressively courting voters in the final days before the election.

As of 1.30am local time (2.30pm Singapore time), Pennsylvania's Department of State reported that almost 1.4 million mail ballots - a little more than half the total - were counted statewide, with 67 per cent for Mr Biden and 32 per cent for Mr Trump. There were 3.1 million Election Day votes counted, with 67 per cent for Mr Trump and 32 per cent for Mr Biden.

Pennsylvania has more than one million votes left to count, Governor Tom Wolf, a Democrat, in a Twitter posting early on Wednesday morning.

In Philadelphia, the commonwealth's most populous county, where 76 per cent of registered voters are Democrats, only 75,755 of the expected 350,000 to 400,000 mailed-in ballots had been counted as of 9pm, with Mr Biden winning 94 per cent of them.

BOTTOM LINE: Philadelphia is expected to resume reporting on mail-in ballots at about 9am on Wednesday (10pm, Singapore time). State officials say a final result should be ready "within days".

Wisconsin

Wisconsin, with 10 electoral votes, is likely to report fuller results in the early morning hours, after election workers struggled with an unprecedented number of mailed-in ballots starting when polls opened on Tuesday morning. The Biden campaign has counted on flipping the state after Mr Trump's narrow win in 2016.

The state's voting system is highly decentralised, with 1,850 municipal clerks who administer elections. Smaller municipalities may finish first, Ms Meagan Wolfe, the state's elections commission administrator, said during a call with reporters on Tuesday night. But the biggest impact will come from a count of Milwaukee, the state's biggest city, where around 169,000 ballots were cast.

BOTTOM LINE: Milwaukee is likely to complete its count of absentee ballots soon, but some other cities also have votes to report.

Michigan

Michigan - another state Mr Trump narrowly won in 2016 - will likely not have final results until Wednesday evening, Secretary of State Jocelyn Benson told reporters. The city of Detroit had a 55 per cent turnout, which equates to more than 250,000 votes.

The state likely won't have final results until later on Wednesday because Detroit is the largest precinct and had a record turnout this year.

Ms Benson did say that other Michigan counties will be reporting in the coming hours, which could give election watchers an idea of where the state is leaning. She said that 3.3 million absentee ballots have been received and are being tabulated and another two million to 2.5 million voted at the polls today.

BOTTOM LINE: "I'm confident we'll have more of an update for Detroit in the morning," said Ms Benson, who added that she expects the full tabulation of every vote in Detroit to be complete by late Wednesday.

Georgia

Some of the biggest counties in Georgia were struggling with counting absentee ballots, tying up results in the reliably Republican state that Mr Biden appeared to be making a strong showing in.

In Fulton County, which includes most of the Democratic stronghold of Atlanta, 71 per cent of precincts had reported by 12.30am (1.30pm, Singapore time). Fulton suffered a setback earlier on Tuesday in counting mailed-in ballots after a water leak forced officials to stop tallying and tens of thousands of ballots were left uncounted.

Votes are also still being counted in neighboring DeKalb County.

Gwinnett County, which has Georgia's second largest population, election officials also struggled with a glitch that was tying up the processing of as many as 80,000 mail-in ballots. By 12.30am, 97 per cent of in-person voting precincts in Gwinnett were reporting.

BOTTOM LINE: Wednesday morning should bring more clarity on the Peach State's results.

North Carolina

North Carolina's race was tight as Wednesday dawned, with Mr Trump leading by about 77,000 votes at 1am (2pm, Singapore time).

About 62 per cent of the state's voters cast ballots before Election Day. More registered Democrats voted early than Republicans, but one-third of the electorate is unaffiliated with either major party. Counting of same-day voting, which is expected to skew Republican, will take longer, and the state has up to nine days to count mail-in ballots sent before Election Day.

In a sign of the delays, just one-third of the precincts in Democratic-leaning Wake County were tallied while in Granville County, where Mrs Hillary Clinton scored a narrow win in 2016, no results were reported. GOP-leaning areas such as Union County near Charlotte had many votes left to be counted as well.

Democrats took some solace in Governor Roy Cooper winning re-election, but it's not clear if that's a signal Mr Biden can flip the traditionally Republican state.

BOTTOM LINE: State officials have said they expect 97 per cent of the vote to be tallied heading into Wednesday morning hours.

Nevada

A final count in Nevada isn't expected for several days as it awaits ballots mailed as late as Election Day to arrive, though it isn't clear how many people waited that long to vote. With about 80 per cent of votes counted, Mr Biden was holding a lead of just under three percentage points.

"Clerks have until Nov 10 to receive mail ballots and until Nov 12 to count them," said Ms Jennifer Russell, a spokeswoman for Nevada's secretary of state.

BOTTOM LINE: The state began posting partial results late Tuesday, with Mr Biden holding a slim lead over Mr Trump. That count, which included early and Election Day voting, will continue to trickle in overnight.