The father of 20-year-old University of Pittsburgh student Sudiksha Konanki, who went missing in the popular Dominican Republic tourist town of Punta Cana while on spring break with friends, said he has asked authorities to widen their investigation.

Konanki was last seen before dawn on March 6 at a beach near the resort where she was staying, according to civil defence officials.

"It's four days, and if she was in water, she would likely have been strewn to shore," her father Subbarayudu Konanki told WTOP-FM.

"She's not found, so we're asking them to investigate multiple options, like kidnapping or abduction."

Authorities were using drones, helicopters and detection dogs on Monday to scour the waters off the island's east coast where she was supposedly last seen, Jensen Sánchez, a civil defence spokesperson, told The Associated Press.

"The search is underway at sea because it's presumed she drowned. According to the boy who was with her, the waves swept her away, but that is under police investigation," he said.

He noted it can take more than a week for a body to surface in warm waters.

Official complaint filed

When her family learned of her disappearance, Subbarayudu Konanki and his wife Sreedevi flew to Punta Cana with two family friends. He and a family friend filed a record of complaint Sunday, asking authorities to widen the investigation.

The complaint notes that the student's belongings, including her phone and wallet, were left with her friends, "which is unusual because she always carried her phone with her."

"In light of these circumstances, I respectfully request that the authorities take immediate steps to investigate not only the possibility of an accidental drowning, but also the possibility of a kidnapping or foul play," he wrote, according to WTOP-FM.

Sudiksha Konanki, a citizen of India, is a U.S. permanent resident from Chantilly, Va., according to the Loudoun County Sheriff's Office, which is working with federal officials and university police in support of the Dominican National Police investigation.

University of Pittsburgh officials are in contact with the family and authorities in Virginia, and have offered their support in the efforts to find the missing student and bring her home safely, the school said in a statement.

Konanki and five other female university students traveled to the Dominican Republic on March 3, according to her dad.

"She wanted to have a nice break with her friends in Punta Cana," he said.