However, police have not spotted anybody moving along the coast so far.
According to police, a fisherman had informed police at about 7 pm yesterday that four persons sailing on two boats were spotted off the coast of Wadala.
"The four persons, who were not familiar with Marathi, were asking the fishermen in Hindi as to where food would be available," a police officer told PTI.
Deputy Police Commissioner Tanaji Gadage, along with his team swung into action and patrolled the coast off the Yellow Gate, Wadala, and Shiwree till 11.30 pm last night, but no suspicious person was found.
"As of now, nothing suspicious was found, but our inquiry is on," Gadage said.
If the person, who informed the police about it was found to be playing mischief, then appropriate action would be initiated against him, police said.