Dockworkers at major ports along the US East and Gulf Coasts began walking off the job early on Tuesday after last-minute negotiations yielded no new labour contract, a stoppage expected to drag on the world's largest economy just ahead of the November presidential election.

A strike at the Port of Virginia "began at 12:01 am", the port said on its website, adding that talks between the International Longshoremen's Association (ILA) and the United States Maritime Alliance (USMX) shipping group "have reached an impasse".

"This is not unique to Virginia," the port of Virginia said. "This is a coast-wide labour action, meaning it is directed at container ports along the US East and Gulf Coasts."

The 85,000 longshore workers have been calling for higher wages and a ban on automating cranes, grates, and moving containers as part of the loading and unloading process.

A possible stoppage had been telegraphed for months, with the odds rising in recent weeks as the two sides described themselves as far apart, with no sign of real progress.

USMX however said late on Monday that it was "hopeful" after the two sides exchanged counteroffers.

But when the six-year contract expired at midnight, there was still no deal.

"Nothing's going to move without us – nothing," ILA President Harold Daggett said on Tuesday outside a port in Elizabeth, New Jersey, according to The New York Times.

The strike comes just weeks before the presidential election and could become a factor if there are shortages. Retailers, auto parts suppliers and produce importers had hoped for a settlement or that US President Joe Biden would intervene and end the strike using the Taft-Hartley Act, which allows him to seek an 80-day cooling off period.

But during an exchange with reporters on Sunday, Biden, who has worked to court union votes for Democrats, said “no” when asked if he planned to intervene in the potential work stoppage.

The walkout marks the ILA's first since 1977 and follows other high-profile strikes at US automakers, Boeing and other employers. The contract directly affects some 25,000 ILA members at 14 large US ports, including New York/New Jersey, Boston, Philadelphia, Savannah, New Orleans and Houston. (AFP/AP)