Outgoing US President Joe Biden warned of a "dangerous" oligarchy forming in America as he delivered his farewell speech and ended a decades-long career in politics.

"Today, an oligarchy is taking shape in America with extreme wealth, power and influence that truly threatens all of our democracy, our fundamental rights and freedoms," he said Wednesday.

Biden, 82, took aim at an ultra-wealthy "techno-industrial complex" that he said could wield unchecked power over Americans.

He also used his final televised address from the White House to issue warnings about climate change and social media misinformation. Speaking from the Oval Office where his family had gathered to watch, he touted his administration's one-term record, citing job creation, infrastructure spending, health care, getting the country out of the pandemic and making the US a safer place, the BBC writes.

He added, however, that "it will take time to feel the full impact of everything we have done together, but the seeds have been planted, they will grow and flourish for decades to come."

Biden wished the incoming Donald Trump administration success, but then issued a series of stark warnings, with the president saying that "so much is at stake right now."

On climate change, he said that "powerful forces want to exert their unchecked influence to eliminate the steps we have taken to address the climate crisis to serve their interests for power and profit."

Regarding disinformation, Biden warned that "Americans are being buried under an avalanche of misinformation and disinformation, enabling the abuse of power."

Closing his speech, Biden called on Americans to "stand guard" of their country.

His farewell speech came on the same day he announced a ceasefire agreement between Israel and Hamas, which he referred to in his opening remarks.

Biden said the negotiations had been some of the most difficult of his career and took credit for helping to reach the agreement.

The agreement will see a ceasefire take effect on January 19, the day before Trump takes office. The incoming president has also taken credit for the deal, saying it was only possible because he won the election in November.