SYDNEY (AFP) - Australian batsman Phil Hughes was in critical condition following emergency surgery on Tuesday after he was knocked out by a short delivery in a freak incident which shocked cricket.

The 25-year-old, who is pressing for a Test recall, crashed to the ground unconscious after the heavy blow to the head and was air-lifted to hospital from Sydney Cricket Ground.

Television images showed the helmeted Hughes, who had scored a composed 63 for South Australia in the Sheffield Shield game, standing dazed before going down face-first following the rising delivery from New South Wales bowler Sean Abbott.

New South Wales players, including Test colleagues David Warner and Brad Haddin, quickly rushed to his side and immediately called for help.

"He is undergoing surgery," said David Faktor, a spokesman for St Vincent's Hospital, where Hughes was taken. "He has sustained a head injury, he is in a critical condition."

A hospital statement later said Hughes was out of surgery but remained in critical condition in intensive care.

Reports said he was in an induced coma and being treated to relieve pressure on his brain from bleeding.

Tim Nielsen from South Australia Cricket read out a statement from the Hughes family outside the hospital.

"The outcome of the surgery is unlikely to be known for the next 24-48 hours," he said. "We would appreciate it if you would look after the family and friends and respect their privacy please."

Cricket Australia said in a live match blog on its website that Hughes had "been leaving the short balls, had a go at this one, misjudged it and was hit in the head. He blacked out and fell badly". The match was abandoned.