Witnesses described a “horrendous” scene as they helped a man who had been stabbed.
The man was taken to hospital with serious injuries following the attack.
One witness saw the man lying in the road and said emergency services were called.
Sussex Police arrived at Whitehawk Close in Whitehawk at 12.45pm yesterday.
The force kept the road cordoned off all afternoon and evidence markers were placed along the close.
The witness told The Argus: “I saw a guy lying out in the road. It was horrendous.
"We put him in the recovery position and phoned 999."
Detectives were at the scene taking pictures.
A bed sheet and scissors were left on the road.
A Sussex Police spokeswoman said: “He was taken to hospital with serious injuries, believed to have been caused by a bladed weapon.
“An urgent investigation is underway to establish the full circumstances of the situation and locate any suspects.
“The public can expect to see an increased police presence in the area at this time.
“Anyone with information is asked to contact Sussex Police either online or by calling 101, quoting serial 675 of 14/07.”
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