Australia Test batsman Phillip Hughes has died aged 25, two days after being hit on the head by a delivery during a domestic match in Sydney.

Australia team doctor Peter Brukner said he passed away in hospital, never regaining consciousness.

Hughes, who also played for Hampshire, Middlesex and Worcestershire, was struck by a ball from Sean Abbott.

"It's an understatement to say we're completely devastated," said Cricket Australia boss James Sutherland.

"The word tragedy gets used too often in sport, but this freak accident is a real life tragedy."

Australia captain Michael Clarke read out a statement on behalf of the Hughes family at a news conference held at St Vincent's Hospital, where the player, who would have been 26 on Sunday, was being treated.

Speaking on behalf of parents Greg and Virginia, sister Megan and brother Jason, he said: "We're devastated by the loss of our much-loved son and brother, Phillip. It's been a very difficult few days.

"Cricket was Phillip's life and we as a family shared that love of the game with him. We would like to thank all the medical and nursing staff at St Vincent's Hospital and Cricket New South Wales medical staff for their great efforts with Phillip. We love you."

A clearly emotional Clarke then stood up and left the room.

Hughes, batting for South Australia, collapsed face first on the ground after being hit by a bouncer from Abbott during a Sheffield Shield game against New South Wales.

Hughes had been wearing a helmet but the ball struck him at the base of the skull, causing the injury.

He had CPR and mouth-to-mouth resuscitation at the ground before being taken to St Vincent's Hospital, where he had a 90-minute operation to relieve pressure on his brain.

Members of the Australian national team, including Clarke, visited Hughes in hospital.

But his death was confirmed in a statement on Thursday.

"It is my sad duty to inform you that a short time ago Phillip Hughes passed away," said Brukner.

"He never regained consciousness following his injury on Tuesday.

"He was not in pain before he passed and was surrounded by his family and close friends.

"As a cricket community, we mourn his loss and extend our deepest sympathies to Phillip's family and friends at this incredibly sad time.

"Cricket Australia kindly asks that the privacy of the Hughes family, players and staff be respected."

Speaking at the news conference, Brukner explained that Hughes had died as a result of "vertebral artery dissection".

He said the artery had been compressed, causing it to split and leading to a "massive bleed" into the brain.

Brukner said the injury was "freakish", adding: "Vertebral artery dissection is incredibly rare. If you look in the literature, there is only 100 cases reported. There is only one previous example caused by a cricket ball."

The Australian flag was lowered to half-mast over the Sydney Cricket Ground where Hughes suffered the horrific injury. Flags were also lowered at the iconic Melbourne Cricket Ground.

Australian Prime Minister Tony Abbott paid tribute to Hughes, describing him as "a young man living out his dreams".

"His death is a very sad day for cricket and a heartbreaking day for his family. What happened has touched millions of Australians," he said.

"For a young life to be cut short playing our national game seems a shocking aberration. He was loved, admired and respected by his team-mates and by legions of cricket fans."

Australia coach Darren Lehmann tweeted: "RIP you little champ, we are all going to miss you! Love, prayers to all the Hughes family."

The England team also released a statement on Twitter, writing: "Our deepest sympathies go out to Phil Hughes' family, friends and team-mates at this incredibly sad time.

"Phil was admired and respected by all he played with and against and will never be forgotten by the cricket community."

Indian icon Sachin Tendulkar, who played alongside Hughes in the Indian Premier League, added: "Shocked to hear about Phil. Sad day for cricket. Deepest condolences to family, friends and well wishers. RIP."

The International Cricket Council (ICC) issued a statement offered its "deepest condolences to the family and friends" of Hughes.

ICC chairman Mr Narayanaswami Srinivasan added: "We are all shocked and saddened with the news of Phillip's passing.

"On behalf of the entire cricket community, I would like to extend my sincere condolences to his family and friends."

Hughes, who had played 26 Tests, made his Test debut at the age of 20 against South Africa in 2009.

In only his second match, he became the youngest batsman to post two centuries in a single Test.

He played county cricket for Hampshire, Middlesex and Worcestershire and shared in what was at the time a world record 10th-wicket partnership of 163 with Ashton Agar against England in the 2013 Ashes series.

Cricket Australia had already decided to abandon the latest round of Sheffield Shield matches following the injury to Hughes.

After his death was announced, cricket officials from Pakistan and New Zealand chose to abandon the second day's play in the third and final Test between the two countries.

"It's a sad day for cricket," Pakistan Cricket Board chairman Shaharyar Khan said in a statement.

New Zealand Cricket chief executive David White added: "Cricket is a family. Quite apart from its super-competitive edge, it is a game of kinship, mateship and friendship; of camaraderie and community."