First Minister Mark Drakeford has warned lockdown will not be eased if incidents and mass gatherings continue to happen.
It comes after two men were detained by police after a mass brawl and large crowds gathered at a beach.
Videos on social media showed large numbers of people at Ogmore-by-Sea in the Vale of Glamorgan, followed by violent scenes.
Responding to the incident on social media the First Minister said: "We will not be able to continue easing restrictions if scenes like last night continue to happen.
"They threaten the health of people in Wales and undermine the sacrifices the majority of people have made during this ongoing crisis."
In Friday's press conference, the First Minister said he wouldn't allow the "ugly actions of a relatively small group of people cast a shadow".
Police detained two men in their 20s and dispersed the crowds.
The council were asked to close the car park but officers had to re-attend at 10:50pm after some of the group returned.
Witnesses have described one person being injured but no victim has come forward.
Police say they are investigating the "unacceptable" incident and appealing for witnesses and mobile footage.
Detective Chief Inspector Tom Moore said: “The scenes at Ogmore-by-Sea were totally unacceptable and the main focus of our investigation will be to identify those who were responsible.
“We believe that a large number of youths have travelled to the area from various areas of South Wales to become involved in serious, violent disorder.
“I am appealing to anyone who can assist our investigation to contact us so we can identify and take action against those involved.
“The local community can also be assured that we will be working with partner agencies and doing everything we can to ensure there is no repeat of this behaviour.”
Piles of rubbish and broken glass was left behind after the gathering which had to be cleared up on Friday morning.
The gathering took place on the hottest day of the year so far when temperatures in Wales reached 31.4°C.
Meanwhile, Vale of Glamorgan council enforcement officer also responded to "hostile and aggressive youths" jumping from cliffs at Rhoose Point, near Barry.
They described the behaviour as "unacceptable" and said "appropriate action" would be taken.
The Police and Crime Commissioner for South Wales, Alun Michael said what happened in Ogmore was "an absolute disgrace." He said social media was partly to blame as that is where people often "get their messaging from" instead of from governments.
He added that people have been tempted into breaking lockdown restrictions through a "contagion of stupidity."
The current lockdown restrictions in Wales mean that people from two different households are able to meet outdoors while keeping at least two metres apart.
The Welsh Government is still asking people to remain local, with the guideline being that people should not travel more than five miles from their homes unless they have to.