Golf: Australian golfer Jason Day collapses at US Open

Jason Day of Australia is tended to by caddie Colin Swatton as he lays on the ninth green after falling due to dizziness during the second round. Photo / AP.

Australian golfer Jason Day has collapsed on the final hole of his second round with a bout of vertigo.

While Day was able to get up after a significant delay and medical attention and close out a round of even-par 70, he was in obvious distress.

The world No.10 is well poised for the weekend, two-under for the tournament and just three shots off the lead.

Day was walking down the ninth, his final hole of the day, when he collapsed.

After a delay of several minutes, he got back to his feet and made a bogey.

Day has been suffering from fatigue and dizzy spells for the better part of a year, withdrawing from last year's World Golf Championship Bridgestone Invitational after a bout and once again having issues in 2015.

He complained of fatigue in the latter part of the Zurich Classic in New Orleans, struggled at the WGC Match Play and the Players Championship and withdrew from the Byron Nelson Championship three weeks ago before it began after struggling with dizzy spells in the Pro-am.

"His head was down, his eyes going back and forth and he said 'I have vertigo, I will be ok"' television analyst and Australia's former major winner Greg Norman said after visiting Day in the scorer's shed.

"Colin Swatton (caddie) said it is exactly what happened at Firestone last year. He went down there and withdrew from the tournament.

"He is a tough kid and it is a little confusing for him as he doesn't know what the issues are.

"There is something there, let's just hope he gets better very very quickly."

It is not yet known if he will be able to continue in Saturday's third round.

The 27-year-old has taken a series of tests over the last month to try to pinpoint the problem but has yet to get an answer.

He was whisked away from the course by medical staff and is being further assessed.

-AAP