Speaking on the steps of the Welsh Government buildings in Cathays Park, Cardiff he said: “It is with great sadness that we learn today of the death of Her Majesty Queen Elizabeth II.
“She has been the only monarch that most of us remember and today the country feels an immense loss.
“Throughout her long and exceptional life, as our longest-reigning monarch, Her Majesty firmly upheld the values and traditions of the British monarchy.
“On behalf of the Welsh Government and people in all parts of Wales I offer our deepest condolences to all Her Majesty’s children and their families on this sad occasion.
“She will be sorely missed by the many organisations in Wales she championed and supported, over so many decades, as patron or president.”
Welsh Conservatives leader Andrew RT Davies said the Queen had an “unrivalled impact” on people across the world.
Mr Davies said: “The sad news of Her Majesty Queen Elizabeth II’s passing will touch many families not just in the United Kingdom, but also across the Commonwealth and the world.
“Many of us will not have known another head of state of our great country.
“For many, she has been as much a part of our families as those who gather each day around the family table.
“Today, there will be an empty chair around those tables, as many will reflect on her 70-year reign and a lifetime of public service.
“Our thoughts and prayers are with the Royal Family at this sad time.
“In the fullness of time, our sadness will give way to the sunshine of memories that her reign has brought to our lives and our great country.”
Mr Davies urged people to “unite” in grief and “take strength that our country and the Commonwealth are better places today for her long reign and life of public service.”
Plaid Cymru Westminster leader, Liz Saville Roberts MP said: “Her Majesty the Queen has been a constant in all our lives during a period of vast changes for Wales, the United Kingdom and the rest of the world.
“She dedicated her life to public service and duty.
“Such values are dear to the people of Wales. May she rest in peace.”
Plaid’s Senedd leader Adam Price tweeted: “Her sense of duty was recognised by millions, and she will be remembered as a figure who provided stability during times of crisis.”
Welsh Liberal Democrat leader Jane Dodds said: “I am deeply saddened to hear of the death of Her Majesty Queen Elizabeth II.
“My thoughts are with the King, her majesty’s other children, grandchildren and all those close to her at this difficult time.
“Her Majesty’s passing, without a doubt, does mark the end of a very long, and indeed a seminal chapter in the history of our nations and for most people her presence has been one of the few constants throughout their lives.
“Throughout her life, Her Majesty served the country with the absolute greatest dedication, honour and dignity.
“From serving in the Auxiliary Territorial Service during World War Two, to taking the time to speak to local school children at the opening of the Senedd last year, she never once shied away from public duty.
“Her life will forever be interlinked with that of a period of great change within the UK and although many today would struggle to recognise the world she had been born into, she always seemed to belong very much here today in the present.
“Her Majesty was always a great friend to Wales and she will be deeply missed within the UK, the Commonwealth and further afield.
“I pray that her journey into the next stage has been peaceful and that she is at rest.”
Bishops of the Church in Wales, including Archbishop of Wales Andrew John, said their prayers are with the royal family.
In a statement, they said: “We will all be mindful of the commitment she made on her 21st birthday in 1947, when she promised her whole life to the service of the people.
“It is a commitment from which she never flinched, and a service which she gave gladly.
“She endured through good times and bad, through celebrations and setbacks in the life of the nation.
“Whenever she was called upon to speak to the nation and the Commonwealth, she spoke in a way which reminded us of who we were, and called us to a greater response and more hopeful future.”
Flags were lowered at all Welsh Government sites including the Senedd on Thursday evening.
Screens in Cardiff city centre displaying pictures of the monarch gathered mourners and onlookers.
Welsh artist Nathan Wyburn paid tribute on Twitter, sharing a digital collage he created using one picture from every year on the throne.
“May she rest in peace,” he wrote.