A 32-year-old woman is in a life-threatening condition after being stabbed at the Notting Hill Carnival, the Metropolitan Police has said.

The force says it is aware of two other people who have been stabbed during the west London festival – including a 29-year-old man and a 24-year-old man.

About 7,000 officers are patrolling this year’s event which is expected to attract about one million people across Sunday and Monday.

Issuing an update on Sunday night, the Met said 90 arrests had been made for a range of offences and “15 officers have been assaulted”.

The alleged crimes included assault on an emergency worker, assault, possession with intent to supply, sexual offences and robbery, the police said.

“Hundreds of thousands of people came to Notting Hill Carnival to enjoy a fantastic celebration,” the Met said.

“Our officers have been on duty working to keep them safe as part of a very carefully planned policing operation.

“Regrettably, a minority came to commit crime and engage in violence.”

The force said a section 60 order, which gives officers additional powers to search suspects, was put in place from Sunday evening until 02:00 BST early on Monday morning.

Ahead of this year’s carnival, the Met described it as a fixture in London’s cultural calendar that was also a “challenging event to police with very dense crowds and a regrettable history of a minority of people using it as an opportunity to commit crime, including violence”.

Commander Charmain Brenyah, the Met’s spokesperson for this year’s event, said as she had grown up not far from where carnival takes place, she had “happy memories of the music, costumes, floats and fantastic atmosphere”.

“Sadly, however, we know that for a minority of people, carnival is an opportunity to commit crime or to seek out violent confrontation,” she said.

“As a police officer on duty in previous years I’ve seen both the carnival I experienced in my youth, but also the other side of the same event when, later in the day, the atmosphere changes in some parts, with floats and costumes giving way to serious violence.”

She added that in the past two years, one person had been killed, 14 others had been stabbed and more than 125 police officers had been assaulted.

About 500 arrests were made at the carnival during those two years.

“These incidents can’t be downplayed or dismissed,” she said.

“It is for that reason that anyone going to carnival will see a very significant policing presence.

“We’re there to keep you safe – if you see us say hello – but we’re also there to intervene decisively against those intent on violence.”

Separately, the London Ambulance Service (LAS) said it has 180 extra staff on duty across the event – most will be clinicians who can get to patients in crowded areas on foot or by bike.

LAS’s Jack Bromley added: “There will be fixed first aid treatment centres and event response teams who operate on foot within an event footprint, jointly staffed by St John Ambulance and LAS.”