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.
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It'll be a dry and fine end to the day, with a dry night then following.
The world bog snorkelling championships returns to Llanwrtyd Wells this weekend.
A cloudy start with a scattering of showers spreading eastwards, allowing some warm sunshine to develop from the west during the afternoon.