* Tokyo 2020 test event shortened over 'extreme heat'
* Triathlon serves as Olympic qualifying event
* Bermuda's Duffy wins after double-disqualification (Updates with race details, background)
By Jack Tarrant
TOKYO, Aug 15 (Reuters) - British triathletes Jessica Learmonth and Georgia Taylor Brown were both disqualified after they crossed the line together following the heat-affected test event for next year's Tokyo Olympics on Thursday.
Learmonth and Taylor Brown held hands as they crossed the line after organisers had earlier halved the distance of the running section to five kilometres because of concerns over the extreme heat.
Bermuda's Flora Duffy, who finished third behind the pair, was elevated to first in the race that also doubled as an Olympic qualifier.
International Triathlon Union (ITU) officials deemed the British pair were in breach of rules that state athletes must not "finish in a contrived tie situation where no effort to separate the finish times has been made".
Duffy was officially awarded the win in a time of 1:40:19. Italy's Alice Betto was second while Britain's Vicky Holland completed the podium.
"The whole point of coming here was to check out the venue, check out the course and see the conditions," Duffy, who missed most of last year with injury, told reporters.
"I love racing in hot and humid weather and that felt pretty good today."
The ITU had decided to reduce the distance of the run section with concerns the weather conditions at the end of the race would have fallen within "extreme levels".
The swimming and cycling segments remained the same after the ITU deemed the water quality and temperature in the Odaiba Marine Park course to be within regulation.
ITU regulations state that the swimming segment must be shortened or cancelled if the water temperature is above 30.9 degrees Celsius but the highest water temperature measured on Thursday was 30.3.
The race began on time at 7:30 a.m. (2230 GMT).
On Wednesday, the ITU had moved Saturday's Paratriathlon World Cup start time forward by one hour to avoid exposing athletes to high temperatures.
The World Cup, a test event for next year's Paralympics, will begin at 6:30 a.m. with all athletes expected to finish the race by 9:30 a.m.
With less than a year to go until the start of the Olympics, how athletes will cope with the extreme heat has been a key concern for organisers and sports bodies.
Soaring temperatures have killed at least 57 people across Japan since late July, highlighting the possible health threat to athletes and fans.
Kyodo News reported last weekend that several athletes were treated for heatstroke at the 2019 World Rowing Junior Championships in Tokyo, which was another test event for Olympic organisers.
Reporting by Jack Tarrant, editing by Pritha Sarkar/Greg Stutchbury