Southampton Town police have closed Long Beach Road in Sag Harbor after a caller reported finding what appeared to be explosive putty.
A person found the substance on the beach, a police spokesman said, and police closed the road alongside it around 1:30 p.m. as a precaution.
The road remained closed two hours later.
Explosive putty is a moldable material that can be detonated.
The spokesman said police were waiting for county assistance to sweep the area and remove the putty.