A massive search is on to track a British astrophysicist who went missing after going for a run in a Greek island, Monday.

The Greek police have mobilized and pressed into service fire vehicles and even a helicopter to search for  35-year-old Natalie Christopher who went missing on Ikaria.

Christopher was visiting the island with her partner from their home in Cyprus. According to the CNN, when her partner woke up on Monday morning, she was nowhere to be found. Upon calling her, she told him she'd gone out for a run. When Christopher didn't return after several hours and had stopped answering her phone, her partner reported her missing. The couple was due to return to Cyprus on Monday.

Police detected a signal from her cell phone Tuesday, about 24 hours after her disappearance, but they couldn't locate her. They also said that on Wednesday morning, the Greek defense ministry was assisting with the search.

Christopher's sister has appealed for anyone with information to assist in the search. However, she has also urged people to not call her.

Christopher's last presence on social media was on Sunday, when she posted images on Facebook of her holiday on the island.

"Beautiful spot for swimming and deep water solo ... had so much fun here today!" she wrote.

Christopher's disappearance is not the first missing persons case this year to haunt Greece. In July, American scientist Suzanne Eaton went missing when she was attending a conference on the island of Crete. Her body was subsequently found in World War II bunker and a 27-year-old man confessed to her murder.

Missing Toddler In this representational photo, police tape seals off a street where authorities are searching a home after three people were arrested in connection with the disappearance of missing chef Claudia Lawrence in York, England, April 22, 2015. Photo: Getty Images/ Christopher Furlong