Brave climber Jessica Biel

Jessica Biel is facing treacherous conditions climbing Mount Kilimanjaro.

The 27-year-old actress and fellow film star Emile Hirsch, 24, are struggling to keep warm as they battle their way up the enormous 19,340 foot climb to raise awareness about the need for clean water worldwide. United Nations Foundation executive Elizabeth Gore said: "It's pretty gnarly. The visibility is only 10 feet in front of you. And it's cold. I've got six layers on. "

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Jess is doing awesome. She continues to bring levity yet seriousness at the same time." The group - who have currently climbed over 16,000 feet - are reportedly taking their minds off the challenge by rapping and playing board games. Elizabeth explained: "We've played every game you can imagine - travel Scrabble, word games. And there is a lot of free-style rapping going on."

The two stars are joined on the trek by musician Lupe Fiasco, 'Home and Away' actress Isabel Lucas and Jacques Cousteau's granddaughter Alexandra. The trek up the African mountain was organised by musician Kenna, whose father suffered from waterborne diseases growing up in Ethiopia.