The emergency unit at University Hospital of Wales is treating adults and children involved in the incident in Rhoose.
The unit has specialist procedures in place for dealing with serious incidents and those have been activated to care for those involved.
The priority now is treating those involved and supporting their families.
More top news
After a spate of injuries, there was some good news for rugby fans today with Jamie Roberts ruled fit and available for selection.
Only a handful of these marine mammals are seen each year but last week a record number were recorded off the coast of North Wales.
Lots of sunshine for you again today, but make no mistake.... it is cold out there!