 Authorities in Japan have warned people not to go up Mount Fuji before the climbing season officially opens in July. They've seen four climbers die at a time when the trails are still closed. Mountain guide Takekawa Shunji explains the risks. It still has some snow in June, so a climber must know that conditions won't be different to those of winter. Overnight lows at the peak this time of year on some days dip below freezing.