Hollywood actress Susan Sarandon has been forced to pull out of an event in support of US presidential hopeful Bernie Sanders after being injured in a fall.

The 73-year-old Academy Award-winner said she suffered concussion, a fractured nose and a “banged up knee” following a “little slip”.

Sarandon shared a selfie to Instagram showing a swelling on her forehead.

The star of films including Thelma & Louise and Lorenzo’s Oil had been due to accompany Mr Sanders at a campaign event in the state of New Hampshire.

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A little slip = concussion, fractured nose, banged up knee. So, looks like I won’t be able to meet the folks in New Hampshire with Senator Sanders tomorrow. I’m really sorry I’ll miss that opportunity but here’s what I’d hoped to say: This is an emergency. Ask the scientists, the farmers, the creatures in the sea. Ask all those who have lost their homes from hurricanes, flood and fire, ask the endless stream of climate refugees, and the people of Flint, San Juan, and Standing Rock. This is a emergency. Ask the mothers who have lost their children to the opioid epidemic or because of the price of insulin. Ask the mothers who have lost their kids to gun violence in schools, in churches, in their bedrooms. This is an emergency. Ask those separated from their families at the border, or those separated from their loved ones by an unjust, racist, for-profit prison system. This is an emergency when our young people have no hope for education, for dream-making, because of insurmountable student debt. When teachers are forced to have additional jobs and when 40 hours of honest labor can still leave you in poverty. When homophobia, Islamaphobia, transphobia and racism take lives, that is an emergency. This is not the time for a “pathway” to or “framework” for incremental change. Emergencies require bold, visionary leadership. Senator Sanders believes in us and that together a better world is possible. He has been fighting for social, racial and economic justice his entire life, long before running for President, often before it was acceptable. Now it’s time for us to fight for him.

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Mr Sanders, the senator for Vermont and a self-described socialist, is among the front-runners for the Democratic party’s presidential nomination ahead of next year’s election.

Sarandon apologised for not being able to make the event and shared the speech she had planned to make at the rally on Instagram.

She said the US is facing an “emergency”, citing climate change fears, the opioid crisis gripping the country and gun violence in schools across the country.

“This is not the time for a ‘pathway’ to or ‘framework’ for incremental change,” she said.

“Emergencies require bold, visionary leadership. Senator Sanders believes in us and that together a better world is possible.

“He has been fighting for social, racial and economic justice his entire life, long before running for President, often before it was acceptable. Now it’s time for us to fight for him.”

Sarandon has a long history of activism and was a vocal campaigner against the Iraq war.

She attracted criticism for refusing to endorse Hillary Clinton when she won the Democratic nomination in 2016.