President Donald Trump has decided to postpone his first post-coronavirus lockdown election rally in Tulsa, Oklahoma, so it does not fall on Juneteenth, the holiday commemorating the end of US slavery.

He tweeted that the June 19 rally would be held a day later out of respect for Juneteenth.

The choice of date had drawn criticism amid nationwide anti-racism protests.

The location was also controversial, as Tulsa saw one of the worst massacres of black people in US history in 1921.

Up to 300 people died when a white mob attacked the prosperous black neighborhood of Greenwood, known as the “Black Wall Street”, with guns and explosives. About 1,000 businesses and homes were also destroyed.

Juneteenth is not a federal holiday, but is widely celebrated by African Americans.

It celebrates the reading of the Emancipation Proclamation to enslaved African Americans in Texas.

Texas was the last state of the Confederacy – the slaveholding southern states that seceded, triggering the Civil War – to receive the proclamation, on June 19, 1865, months after the end of the war.

President Trump initially defended the timing of his rally, telling Fox News: “Think about it as a celebration. My rally is a celebration. In the history of politics, I think I can say there’s never been any group or any person that’s had rallies like I do.”

However, critics accused the president of disrespecting the date and the significance of Tulsa to US history.

Explaining the decision to move his rally, President Trump tweeted: “Many of my African American friends and supporters have reached out to suggest that we consider changing the date out of respect for this Holiday, and in observance of this important occasion and all that it represents. I have therefore decided to move our rally to Saturday, June 20th, in order to honor their requests…”

The “Make America Great Again” rally in Tulsa will be Donald Trump’s first campaign event since March 2, when the coronavirus pandemic put a halt to mass gatherings.

President Trump is seeking re-election in November 2020, but polls show him lagging behind his Democratic rival, Joe Biden.

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Campaign rallies are seen as a key method of energizing his base, and Oklahoma is traditionally a Republican-voting state.

The event will proceed against a backdrop of ongoing protests against racial inequality and police brutality, triggered by the death of African American man George Floyd on May 25. George Floyd, who was unarmed, died in police custody in Minneapolis, Minnesota after a policeman knelt on his neck for almost nine minutes.

The rally is being held in a 19,000-seat indoor arena, and concerns have been raised about the potential risks.

Oklahoma has one of the US lowest infection rates, and businesses are reopening – but the state’s Governor Kevin Stitt has urged residents to keep social distancing and to “minimize time spent in crowded environments”.

People buying tickets for the Tulsa rally online have to click on a waiver confirming that they “voluntarily assume all risks related to exposure to Covid-19” and will not hold the president’s campaign responsible for “any illness or injury”.

President Trump has announced he plans to hold further events in Florida, Texas, North Carolina and Arizona.