Police closed a three-mile stretch of beach yesterday after a large number of unidentified "white granules" washed ashore.
A specialist unit has been sent to test the substance at Hunmanby, near Filey, North Yorkshire Police said. The substance is described as "white granules of an unknown nature".
"Until we have established the nature of the granules and are satisfied that they are not harmful to anyone, the beach will remain closed," a police spokeswoman said.
Officers were called by the Coastguard at around 1.45pm after the granules were washed up on the shoreline. Police and other agencies have been clearing the beach.