The Coast Guard and Mumbai Police were on alert after fishermen reported sighting two unidentified speedboats Sunday afternoon off the north Mumbai coast, an official said.
Some fishermen saw the speedboats around 110 km to the north near Tarapur, where sensitive installations of national importance are located. They sighted the mystery boats off the Satpati coast in Palghar sub-district of Thane district, the official said.
The fishermen informed Mumbai Police, who in turn alerted the Coast Guard headquarters, according to the official.
"We are making investigations and checking out the antecedents of the speedboats and where they could have gone," the official said.
The Coast Guard and Mumbai Police were in a state of high alert on the entire coastal Konkan region following the incident.
The terrorists, who attacked Mumbai Nov 26, had landed in Mumbai through the porous Arabian Sea routes.