London-based Varsha Maisuria was on a skydiving plane which crashed off a popular tourist beach in Puerto Vallarta as holidaymakers looked on in horror.
The 42-year-old and her instructor Robin Ballachey are understood to have become entangled with the Cessna 180 aircraft as they left the plane on a tandem skydive.
The pilot and two male passengers survived but search and rescue teams are still working to find Maisuria and US national Ballachey after the crash last week.
"We are aware of a British national missing in Mexico and we are providing consular assistance," said a Foreign Office spokesperson.
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Maisuria had been on holiday near the resort with a friend.
She had signed up for her first-ever skydiving trip with SkyDive Vallarta before her scheduled return flight on May 9.
Her younger brother, who asked not to be named, told 'Evening Standard': "We are absolutely distraught. She was the only daughter and the eldest child in our family.
"It happened next to one of the leading resorts in Mexico and we have been contacted by some holidaymakers who said they saw the whole thing.
Holidaymaker Mary O'Grady, from San Francisco, wrote on Facebook: "I watched this terrible tragedy unfold on Thursday while on vacation in Mexico. I am still in shock.