Authorities in Maryland were searching on Friday for the daughter and a grandson of the former lieutenant governor Kathleen Kennedy Townsend, after a canoe they were paddling in the Chesapeake Bay did not return to shore.

Governor Larry Hogan identified the missing people as Maeve Kennedy Townsend McKean, 40, and her eight-year-old son, Gideon Joseph Kennedy McKean.

Kennedy Townsend, who served two terms as lieutenant governor, is the eldest daughter of Robert F Kennedy, who was US attorney general, a New York senator and a candidate for the Democratic presidential nomination in 1968, the year in which he was assassinated in Los Angeles. She is a niece of the 35th president, John F Kennedy, who was shot dead in Dallas in 1963.

“I reached out to and spoke with Lt Gov Townsend this morning and on behalf of the people of Maryland I expressed our most heartfelt sympathies and prayers to her and to her entire family during this difficult time,” Hogan said.

The search started on Thursday afternoon after the state natural resources police responded to a report of two people in a canoe in the Chesapeake Bay who appeared to be overtaken by strong winds.

A statement from the agency, which did not name the missing people, said they may have been paddling the canoe from a home in Shady Side, Maryland, to retrieve a ball and were unable to paddle back to shore.

An overturned canoe matching the one used by the missing people was found on Thursday night, the agency said.

Maeve McKean, a public health and human rights lawyer, has been executive director of the Georgetown University Global Health Initiative. The initiative’s website says her work focuses on “the intersection of global health and human rights”.

McKean was previously an associate research professor at the City University of New York School of Public Health.

“News of this tragedy hit me and my family hard this morning,” said Steuart Pittman, the Anne Arundel county executive. “We are holding Kathleen and her family in the light, and holding our own loved ones a little closer as we reflect on their pain and their loss.”

Maryland state police, the US Coast Guard and local police and fire departments joined in the search.