Upper Street in Islington has been closed following the crash, which saw a vehicle plough into Pera Schnitzel Garden at around 7.45am this morning.
One driver, a man in his 20s, was arrested on suspicion of causing serious injury by dangerous driving, police have said.
Officers, ambulance crews and firefighters rushed to the scene near Islington Town Hall where four people were treated.
The emergency crews rushed two of the injured to a major trauma centre, while the other two were taken to hospital.
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Ambulance statement in full
A London Ambulance Service spokesperson said: "We were called at 7.57am this morning (Thursday 10 April) to reports of a road traffic collision in Upper Street, Islington.
"We sent a number of resources to the scene, including ambulance crews, a paramedic in a fast response car, an incident response officer and London’s Air Ambulance.
"The first of our crews arrived in one minute.
"Our crews treated four patients at the scene, before taking two to a London major trauma centre and two to hospital."
Man and son pinned down alleged driver who tried to run away from the scene
A man and his son who witnessed the horror crash in Islington have described how they chased down a driver who was allegedly trying to run away from the scene.
An employee at London-based maintenance company Gilmartins said he and his son managed to pin down a man before the police arrived.
The father, who did not want to be named, told the Metro: “My son got to him and started hitting him but it wasn’t doing anything.
“Then he hit my son in the face and I pinned him down. It felt like forever for the police to come.
“Everyone was standing there and watching.”
Brasserie plans to reopen tomorrow
In an Instagram story, Pera Schnitzel Garden said: “There was an accident right in front of our shop today, and unfortunately, we’ve learned that there were some injuries. We’re sending our heartfelt wishes for a speedy recovery to everyone involved.
“We’ve closed for the day as a result of the incident. Thank you for your understanding, and we’re truly sorry for the inconvenience.
“Take care, and we hope to see you tomorrow.”
Woman 'fighting for life' as driver arrested
Scotland Yard said in an update: “Police were called to a collision involving two cars and a building on Upper Street, Islington at around 07:58hrs on Thursday, April 10.
“One driver, a man in his 20s, was arrested on suspicion of causing serious injury by dangerous driving.
“He was taken to hospital with non-life-threatening and life-changing injuries.
“The driver of the other car, a man, and a female passenger in her 40s were taken to hospital. The female remains in a life-threatening or life-changing condition.
“The road remains closed for investigation and recovery. Enquiries continue.”
'People screaming and running away'
Dee, a store manager at Superette, told The Standard: “I heard the crash.
“I didn’t see it, but I’ve heard an accident on this road before so I knew what it was.
“There was a loud sound. I looked out and there were people screaming and running away.”
“It looked like there was a fight at first, it was strange.”
'Car collided with pedestrian'
A London Fire Brigade spokesman said: “Two cars collided and a third car collided with a building and a pedestrian.
“Four people were taken to hospital by London Ambulance Service.”
'Debris everywhere'
“The accident has spread debris across Upper Street,” The Standard’s news reporter Megan Howe reports from the scene of the crash.
“Three police vehicles remain on site following the collision this morning.
“Surrounding businesses appear to have evacuated.”
Photos from the scene
Pictures from the scene show several cordons in place as the incident is dealt with by officers.
A black car is seen crashed into the restaurant, as well as a five-door hatchback on the road with its bonnet smashed.
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Car 'crashed into Mediterranean brasserie'
The crash saw a vehicle plough into Pera Schnitzel Garden, which describes itself as “Turkish-run restaurant with warm decor, exposed bricks and outdoor dining, open from breakfast”.
It sits toward the Highbury & Islington end of Upper Street, opposite Islington Town Hall.