At least 19 children and two adults have been reported dead after a teenage gunman opened fire at Robb Elementary School in Uvalde on Tuesday.
The shooting is the deadliest at a US primary school since the infamous Sandy Hook shooting in Newtown, Connecticut, in which 20 children and six adults were killed almost a decade ago.
"As you all are aware there was another mass shooting today, this time in my home town of Uvalde, Texas," McConaughey said.
"Once again, we have tragically proven that we are failing to be responsible for the rights our freedoms grant us.
"This is an epidemic we can control, and whichever side of the aisle we may stand on, we all know we can do better.
"We must do better.
Uvalde, Texas, USA. pic.twitter.com/0iULRGtREm— Matthew McConaughey (@McConaughey) May 25, 2022
"Action must be taken so that no parent has to experience what the parents in Uvalde and the others before them have endured.
"And to those who dropped off their loved ones today not knowing it was goodbye, no words can comprehend or heal your loss, but if prayers can provide comfort, we will keep them coming."
James Corden, Taylor Swift, Amy Schumer and Chris Evans were also among the famous faces expressing "rage and grief" in the wake of Tuesday's atrocity.
Addressing the shooting in a monologue on The Late Late Show on US television, Corden said that on the issue of gun laws, America is "one of the most backward places in the world".
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"When I dropped my kids off at school this morning and kissed them goodbye, it doesn't cross your mind that that could ever be the last goodbye," he said.
"And the thought of that phone call, that your child is the victim in a mass shooting is beyond comprehension as a human being."
Swift shared a video of Golden State Warriors coach Steve Kerr, who delivered an emotional message in a press conference before the NBA Western Conference finals.
"Filled with rage and grief, and so broken by the murders in Uvalde," she wrote in a tweet.
Filled with rage and grief, and so broken by the murders in Uvalde. By Buffalo, Laguna Woods and so many others. By the ways in which we, as a nation, have become conditioned to unfathomable and unbearable heartbreak. Steve's words ring so true and cut so deep. https://t.co/Rb5uwSTxty— Taylor Swift (@taylorswift13) May 25, 2022
"By Buffalo, Laguna Woods and so many others. By the ways in which we, as a nation, have become conditioned to unfathomable and unbearable heartbreak.
"Steve's words ring so true and cut so deep."
Oscars co-host Schumer said: "We are grieving with the Uvalde community, a predominantly Latinx community, and everyone else impacted by yet another senseless act of violence in our schools.
"This is yet another tragic example of how pervasive this public health crisis is in our country."
Source: Press Association