Campaigners are cranking up their efforts on the final weekend before the 2018 US mid-term elections, with both Republicans and Democrats warning of dire consequences should they lose.

US president Donald Trump is criss-crossing the country to drum up support for his party, while Democrats are relying on former president Barack Obama and entertainers like Jimmy Buffett in Florida to push their cause.

Candidates and volunteers are knocking on doors, holding rallies and making pitches by phone as dozens of races around America go down to the wire.

Democrats are counting on wresting control of the US house of representatives from Republicans, and hoping for a long-shot series of wins to take back the senate as well.

However, Republicans are optimistic they can gain seats in a senate map heavy on red states, and have not given up on holding the house.

Mike PenceUS vice president Mike Pence speaks at a campaign rally in Florida (AP)

The race is concluding in the shadow of a bomb plot targeting Democratic leaders and the worst anti-Semitic shooting in American history.

Both campaigns have pulled out their heavy hitters. Mr Trump has held a rally in Montana for Republican senate candidate Matt Rosendale, who is challenging Democratic senator Jon Tester. The president will then hold another rally for Republican candidates in Florida.

US vice president Mike Pence has travelled from Kansas to Wisconsin to Florida to push the Republican vote.

Former president Barack Obama’s national campaign tour has taken a somewhat unusual path, with an Indiana rally for senator Joe Donnelly, who has sounded far more like Donald Trump.

Barack ObamaBarack Obama campaigns in Atlanta (AP)

Mr Obama’s rally for the Democratic senator in Gary will be sandwiched between his successor’s trips to the state on Friday and Monday on behalf of the opposing Republican senate candidate Mike Braun.

In West Palm Beach, Florida, three miles from Mr Trump’s Mar-a-Lago estate, singer Jimmy Buffet tried to fire up local Democrats for gubernatorial candidate Andrew Gillum and senator Bill Nelson.

He played a version of the song Margaritaville, slamming the state’s Republican governor, Rick Scott, who is running against Mr Nelson for the senate, over an algae infestation which has killed millions of fish and closed beaches along the state’s western coast.