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World champion decathlete Kevin Mayer says holding the World Athletics Championships in Doha is a "disaster".

The championships started on Friday but 28 runners dropped out of the women's marathon because of 32C temperatures even though it was held at midnight.

Crowds in the Khalifa International Stadium have so far been sparse.

"We can all see it's a disaster, there is no-one in the stands, and the heat has not been adapted at all," the French world record holder, 27, said.

"There have already been nearly 30 withdrawals in the women's marathon. It's sad.

"We have to leave reason aside and more concentrate on the passion, because if not I would have boycotted these championships.

"We haven't really prioritised athletes when organising the championships here. It makes it difficult."

The women's marathon was run in 70% humidity as 28 runners dropped out, including Britain's Charlotte Purdue, from a starting field of 68.

On Saturday athletics' governing body the IAAF released an update confirming 30 athletes had visited the medical centre after racing. "A small number were kept under observation and one athlete was referred to the hospital for observation but later released," it said.

It also said the number of athletes failing to complete the race was "comparable to the completion rate at previous World Championships in Tokyo (1991) and Moscow (2013)".

Track and field athletes will be aided by an air-conditioned stadium in Doha, which IAAF president Lord Coe said reduces the temperature to 23C. However the marathon and walking races are held outside.

The men's and women's 50km walks are set to begin at 23:30 local time on Saturday. When providing its update on Saturday, the IAAF confirmed the race would go ahead as it expected the weather to be "slightly improved on last night".

Before the women's marathon was held, the organisation issued a statement saying it had "done everything possible to minimise the heat-related risks" and that the race would be "run at an acceptable level of health risk".

It said the same measures would be in place for the 50km walk races.

France's Yohann Diniz will be attempting to retain his world title in the 50km walk but said: "I am extremely upset. If we were in the stadium we would have normal conditions, but outside they have placed us in a furnace, which is just not possible.

"They are making us guinea pigs."