Prominent Black Lives Matter activist Sasha Johnson is critically ill after being shot in the head, her party says.
The Taking the Initiative Party (TTIP) said she was being treated in intensive care after being "brutally attacked" in the early hours of Sunday.
The 27-year-old has life-threatening injuries following the shooting on Consort Road, in Peckham, south London.
TTIP said Ms Johnson had undergone an operation and remained in critical care, in recovery post-surgery.
A vigil was held in Ruskin Park, close to King's College Hospital, where Ms Johnson is being treated.
Well-wishers played African drums and prayed for Ms Johnson to pull through.
One speaker told the crowd: "In every community there are good eggs and bad eggs and we have to make sure those bad eggs are held accountable for their actions.
"Because it's not acceptable for those bad eggs to be attacking our warriors - be they male or female.
"Warriors who are out there every day without pay working for our families, working for our communities."
Police said at this stage there was no evidence the attack was targeted.
After fears grew among other activists that it was a targeted attack, Charles Gordon, one of TTIP's founding members said: "I would like to say that we need to stay cautious and aware; the truth is that we don't know what has happened here."
A party spokesman said: "Whilst we understand there is much speculation around the nature of the incident, our priority is Sasha's health and recovery."
Detectives said there was currently nothing to suggest the shooting victim had received any credible threats against her, and have appealed for witnesses.
They have not confirmed her identity.
Earlier, Imarn Ayton, a friend of Ms Johnson's, told the BBC doctors had carried out surgery on her fellow activist, which had gone well and she was "now with her parents".
She said Ms Johnson had been at a party or gathering when she was injured but she did not believe "she was the intended victim".
"As far as I am aware... this incident is more related to rival gangs as opposed to her activism," Ms Ayton said.
Detectives from the Met's Specialist Crime Command have been investigating at the scene and the surrounding area and are pursuing a number of lines of inquiry.
It is believed the shooting happened near a house where a party was taking place and a number of people may have been in the area, a Met Police statement said.
The Taking the Initiative Party said the attack followed "numerous death threats".
Det Ch Insp Jimi Tele said: "This was a shocking incident that has left a young woman with very serious injuries. Our thoughts are with her family who are being provided with support at this terribly difficult time."
He added: "If you saw anything suspicious in the Consort Road area in the early hours of Sunday morning, or if you have heard information since that could help detectives, it is crucial that you get in touch."
Dr Darren Henry, who knew Ms Johnson through community activism campaigns, called on those speculating about the shooting to "let the police do their jobs".
"Like any shocking or horrendous crime in our community, we hope that the offenders are brought to justice and that there is no bias and no racism.
"Let the police do their watching and monitoring, but we are out here as well doing our watching and our monitoring."
Tributes on social media have been pouring in from all over the world since the shocking attack on the young mother.
Tamika Mallory, a well-known US activist posted on her Instagram account: "Pull through sis! People think it's a game out here. Smh. #SashaJohnson", while Labour MP for Tottenham David Lammy tweeted: "This is gut wrenching. Praying for Sasha Johnson, her family and friends that she makes a full recovery #BlackLivesMatter".
And Harriet Harman, the Labour MP for Camberwell and Peckham, tweeted: "Whoever carried out this dreadful shooting of Sasha Johnson needs to be caught quickly. Give any info you have to MPSSouthwark. Reported death threats will need to be investigated. Wishing her a full recovery. With thanks to the NHS for much needed expertise and care."
Ms Johnson was a well known anti-racism campaigner who organised a Black Lives Matter protest last summer, in her home city of Oxford.
Many have praised her courage and determination to stand up for the rights of black people, tirelessly calling out injustices and inequality.
Ms Johnson has previously spoken about living in a society where her black sons would be accepted and which had a better system that could help them grow. She said she was determined to carry on campaigning and wanted to make a difference within her own community.
Ms Johnson, who works in community activism and community support and got a first in social care from Ruskin College in Oxford, has been a leading figure in the Black Lives Matter movement in the UK and is a member of the Taking the Initiative Party's leadership committee.
In its manifesto, the party describes itself as aiming "to create real change in communities across the UK by setting the agenda in government".
It said it wanted to do this by putting forward "exceptional candidates who truly represent their communities, winning seats to create a Parliament that looks like the society it leads".
In a statement on Instagram, the party said Ms Johnson is a mother of two and a "powerful voice" who has always been fighting for black people and against the injustices that affect the black community.
"Let's all come together and pray for Sasha, pray for her recovery and show our support to her family and loved ones," the statement said.
Black Lives Matters UK said it was shocked by the shooting of "a young mother and fearless political campaigner who was at the forefront of many BLM protests last summer".
It said that while she was not part of the organisation, "she impressively founded a new Black-led political party and was dedicated to resist anti-Black racism".
The group added: "Any attempt to intimidate or silence her, is an attack on all of us."