Police, fire and ambulance crews are at the scene of an ongoing incident in Pickford Hill, Harpenden.
The situation, which has escalated throughout the day, began at around 6.45am today, when police were called to a disturbance at the flats in Pickford Hill.
A police spokesperson said: "Officers arrived at the scene to find that a man had barricaded himself inside the property, raising concerns for both his welfare and the safety of the emergency services who were in attendance.
"There is still a heavy emergency services presence at the scene as this incident is ongoing.
"There is a police cordon in place and several residents have been evacuated as a precaution.
"We would ask the public to please avoid the area where possible."
Since, the nearby Sauncey Wood School has closed early, and residents who have been evacuated from their homes have been offered shelter in the school hall.
A cordon was put in place in Pickford Hill, and was later extended back to Fulmore Close.
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