President Joe Biden on Tuesday called out what he branded the "poison" of white supremacist ideology behind a deadly mass shooting in Buffalo, New York, and said that racism is being stoked for political gain.

Speaking in the city where a white teen is accused of murdering 10 African Americans in a neighborhood supermarket, Biden said: "What happened here is simple and straightforward terrorism. Domestic terrorism."

"White supremacy is a poison running through our body politic, and it's been allowed to fester right in front of our eyes," Biden said, condemning "those who spread the lie for power, for political gain and for profit".

In a searing speech that also called for restrictions on ownership of assault-style rifles, Biden listed the victims, fighting tears as he recounted how one of the dead, named as 53-year-old Andre Mackniel, had been buying a birthday cake for his three-year-old son when the gunman entered the store.

Biden's harshest comments were directed at what he described as the "perverse ideology" of white supremacists that police say inspired the shooter.

In a manifesto, the alleged mass killer referred to the so-called "replacement theory" which claims the existence of a leftist plot to overwhelm the white population with non-white immigrants.

Biden described "a hate that through the media and politics [and] the internet has radicalised angry, alienated, lost and isolated individuals into falsely believing that they will be replaced – that's the word, replaced – by 'the other’”.

"No more. I mean no more. We need to say as clearly and forcefully as we can that the ideology of white supremacy has no place in America," he said to applause.

Payton Gendron, the 18-year-old murder suspect, planned the shooting for months – and scoped out the location ahead of time, according to a stream of posts attributed to him on social media sites.

Gendron first wrote about killing Black people in December and decided to target the Buffalo store based on its large surrounding African American population, according to US media analysis of hundreds of pages of messages.

Earlier on Tuesday, Biden and his wife Jill, laid a bouquet at a makeshift memorial outside the supermarket where the slaughter took place. (AFP)