Beyonce has made a rare political appearance, as she hugged Kamala Harris at a presidential campaign rally, telling voters: "We need to sing a new song."

While she did not perform - unlike in 2016 when she sang at a rally for Hillary Clinton in Cleveland - she spoke as Ms Harris warned that her Republican rival for the White House wants women's rights to be further eroded.

"I'm not here as a celebrity, I'm not here as a politician. I'm here as a mother," Beyonce told the crowd in Houston, Texas, as she endorsed the US vice president.

"A mother who cares deeply about the world my children and all of our children live in, a world where we have the freedom to control our bodies, a world where we're not divided."

"Imagine our daughters growing up seeing what's possible with no ceilings, no limitations," the US singer continued. "We must vote, and we need you."

Beyonce was joined onstage by her Destiny's Child bandmate, Kelly Rowland, and introduced Democratic candidate Ms Harris as the "next president of the United States".

Houston is Beyonce's hometown, and Ms Harris's presidential campaign has taken on Beyonce's song Freedom, a track from her 2016 album Lemonade, as its anthem, first using the music in July.

Beyonce gave permission to Vice President Harris to use the song, which samples two John and Alan Lomax recordings that document America's segregation history.

The rally took place in Texas to highlight the growing medical fallout from the state's strict abortion ban. Abortion is illegal in almost all cases, with exceptions for if the mother's life is at risk.

But the ambiguous way the law is written means harmful pregnancies do not explicitly constitute an exception. As a result, the state's infant death rate has increased, more babies have died of birth defects and maternal mortality has risen.

Ms Harris was joined at the rally by women who have nearly died from pregnancy complications. In some states, doctors face criminal charges if they provide medical care to women in life-threatening situations.

"For anyone watching from another state, if you think you are protected from Trump abortion bans because you live in Michigan, Pennsylvania, Nevada, New York, California, or any state where voters or legislators have protected reproductive freedom, please know: No one is protected," Ms Harris warned.

"Because a Donald Trump national ban will outlaw abortion in every single state."

Mr Trump has been inconsistent with his message on abortion and reproductive rights - though he has repeatedly said he would veto a national ban.

He was also in Texas on Friday, where he said he would break records for the number of people deported from the US if he won.