A hotel was evacuated after a water main burst near King's Cross station in the early hours of Sunday morning.
London Fire Brigade (LFB) 8 fire stations and approximately 60 firefighters responded to the incident, which affected an area of approximately 250 square meters on Bentonville Road.
Around 20 people from a nearby hotel were evacuated by staff due to flooding, LFB said.
The brigade was called at 04:07 BST, and mobile flood barriers and specialist water rescue teams were dispatched to the scene.
Bentonville Road is closed to traffic between Benton Rise and King's Cross Road.
Islington Council has urged people to avoid the area while crews respond.
Transport for London 11 bus routes were diverted on Sunday morning.
They are bus routes 17, 30, 46, 63, 73, 91, 205, 214, 259, 390 and 476.
Thames water Contacted for comment. In an update to customers on Sunday morning, it said: “We're sorry if you were affected by the recent burst pipe on Bentonville Road.”
It said engineers were on site and “working hard to get things back to normal soon”.
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Support crews were also “on their way” to help customers with low pressure or no water.
Tina Hodgkinson, who lives on Killick Street off Bentonville Road, said she woke up at 04:00 to what she thought was heavy rain.
“I looked out the window and it wasn't raining, but I saw this stream on Bentonville Road,” he told the BBC.
He said a cordon had been put in place on the street connected to Pentonville Road, and his home was not affected by flooding or water damage on Sunday morning.
LFB Firefighters are using a drone to survey the flooded area, and traffic in the local area will be “severely affected,” he said.
Crews from Euston, Islington, Soho and surrounding fire stations attended the scene on Sunday morning.
The Metropolitan Police said officers were assisting fire crews, while the council said members of its emergency response team were also on site.