New York: Former US vice-president Joe Biden, the Democrat most likely to take on Donald Trump in the 2020 presidential election, has backed an Australian-style gun buyback program following America's latest spate of deadly mass shootings.

Fellow presidential candidate Beto O'Rourke also came out in support of a buyback program to reduce the number of assault weapons on American streets.

Former vice-president Joe Biden said he would implement a gun buyback program if elected president in 2020. Credit:AP

O'Rourke is a former congressman from El Paso, where a white supremacist gunned down 22 people at the weekend. Nine people were shot dead in Dayton, Ohio, on Sunday morning and four people were killed at a garlic festival in California last week.

When asked how he would reduce the huge number of assault weapons in circulation in the US, Biden told CNN: "What I would do is I would institute a national buyback program.