Europe will need to rethink its support of Ukraine if Donald Trump is elected president of the United States, Hungarian Prime Minister Viktor Orban said on Sunday, as the continent "will not be able to bear the burdens of the war alone".

Orban opposes military aid to Ukraine and has made clear he thinks Trump shares his views and would negotiate a peace settlement for Ukraine.

He backs former president Trump, the Republican candidate, to beat Democratic candidate Kamala Harris in Tuesday's US election.

"We (in Europe) need to realise that if there will be a pro-peace president in America, which I not only believe in but I also read the numbers that way... if what we expect happens and America becomes pro-peace, then Europe cannot remain pro-war," Orban said.

Ukraine will be high on the agenda when European leaders meet in Budapest in the coming week, he said, referring to a European Political Community meeting and a more informal meeting of EU leaders due to take place.

"Europe cannot bear the burden of [the war] alone, and if Americans switch to peace, then we also need to adapt, and this is what we will discuss in Budapest," Orban said.

Europe is jittery about how the outcome of the US election will affect the war in Ukraine and the continent's security.

Orban has angered Brussels with his close ties to Russia and opposition to aid for Ukraine.

Hungary's foreign minister Peter Szijjarto said in July that the Hungarian government sees Trump as a "chance for peace" in Ukraine.

In July, Orban said his team was assisting Trump's aides with policies on families and migration. On Thursday, he called Trump to wish him good luck ahead of Tuesday's election. (Reuters)