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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A fairly grey and cloudy start with showers. Improving during the morning with sunny spells developing and showers becoming isolated.
It comes after three men were jailed for helping a Cardiff teenager join ISIS.
Clear skies will continue for a time allowing temperatures to drop to freezing in many places. Cloud developing during the early hours.