A number of people were reported to have been on the boat at the time.
Multiple agencies have been deployed including police, fire, ambulance, the air ambulance, coastguard and search and rescue teams.
Two people were safely recovered from the water and have been checked over and discharged by paramedics at the scene.
Two people have been recovered and taken to Derriford Hospital for treatment. Their conditions are not confirmed.
A further two people remain missing at this time and searches are ongoing.
Next-of-kin have been informed.
The boat is being secured and the scene is being managed by police.
A road closure has been put in place at the activity centre to allow access for the relevant services.