Offices were evacuated and a large cordon was in place amid a gas leak in King's Cross.
Emergency services were called to the area just before 1pm.
Office buildings in the area, including those of the Guardian newspaper, were evacuated.
One person wrote on social media: "In the midst of a huge evacuation near King's Cross - big gas main has been hit!"
Another saw the benefits, posting: "#kingscross closures due to huge gas leak. Loads of evacuees fill the sunlit pub gardens."
Scotland Yard confirmed buildings had been evacuated in York Road, King's Cross, due to a suspected gas leak on a building site.
Nearby Wharfdale Road has also been sealed off following an alert around 12.40pm.
A Met Police spokesman urged people to avoid the area.
London Fire Brigade have also been called to the scene to assist police officers, a spokeswoman confirmed.
York Way was re-opened shortly after 2pm.
A spokesman for the National Grid said: "A gas service pipe was damaged while third party builders were working on a development in York Way.
"We were called at 12.48pm on Thursday and our engineers have disconnected the supply and made safe."
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