Police said they were called to reports of a “large number of people attempting to force entry to the venue”, where Afrobeat artist Asake was performing.
The Nigerian musician was forced to abandon the gig after performing three songs and released a statement saying his “heart is with those who were injured”.
His manager, Stephen Nana, told Sky News he was “completely speechless and lost for words” after Mr Hutchinson’s death was announced.
“We only came to entertain and perform. Never thought that anything like this would happen.”
Metropolitan Police Chief Superintendent Colin Wingrove said: “It is devastating news that a second person has lost their life following the events on Thursday.
“I wish to express my heartfelt condolences to Gaby’s family at this unimaginably difficult time.”
The Met Police have set up an online portal for people to submit information, photographs and videos of the incident, which is believed to have been seen by around 4,000 witnesses. Anyone who can help is urged to come forward.
The force said in a statement: “In the disorder, a number of people suffered serious crush injuries and required medical attention.
“Police are appealing to anyone who attended the venue to come forward with valuable information.”
An incident during which an officer was “apparently seen to push a member of the public” is currently under review by the force’s Directorate of Professional Standards.
An IOPC spokesperson said it is aware of the incident, adding: “We will assess the available information, including footage of the incident, to determine what further action may be required.”
Met Police Gold Commander Ade Adelekan said that where force has been used by officers, “those officers know they have to be accountable for their actions”.
All material, including body-worn video footage from those at the scene, will be looked at by the Directorate of Professional Standards.
‘I won’t rest until we have answers’
London Mayor Sadiq Khan said City Hall is in contact with venues and authorities across the capital to make sure “nothing like this happens again”.
Mr Khan said he was “devastated” by Mr Hutchinson’s death and extended his “heartfelt condolences” to family and loved ones.
He added: “I won’t rest until we have the answers all those impacted by the tragic Brixton incident need and deserve.”
In a statement on Monday, Brixton Academy also offered its “heartfelt condolences”.
“We continue to be devastated by the tragic situation and are fully supporting the ongoing investigation,” the venue said.
Asake, real name Ahmed Ololade, was recently nominated for BBC Radio 1’s Sound of 2023 award – for artists breaking through in the UK.
He urged fans not to turn up without a valid ticket ahead of his performance, one of three sold-out shows at the 4,921-standing capacity venue.
An earlier report, based on information from the Metropolitan Police, stated the second person who died was Gabrielle Hutchinson.
This story has now been updated to reflect Mr Hutchison’s chosen pronouns, following an update from the force.