Video footage shows a heavy police presence in the area.
Unconfirmed reports claim the man shot a woman while they were driving in a car and then jumped out.
Fire officials said she was taken to South Shore Hospital.
The extent of her injuries is unclear.
It is believed the shooter ran into a heavily-wooded area along Route 3A.
A perimeter has been set up while the authorities search for the man with a state police helicopters and K9 teams.
Volleyball team students are currently on lockdown at Marshfield High School.