A Bronx man got on a plane to Thailand after carrying his dead 7-month-old baby around New York City in a backpack and throwing the boy's body into the East River near the Brooklyn Bridge and other tourist hotspots, police said on Wednesday.

Thai authorities stopped James Currie, 37, when he landed in Bangkok and blocked him from entering the country, New York Police Department chief of detectives Dermot Shea said. He will be returned to New York within days to face a felony charge of concealment of a human corpse, Shea said.

The boy's body was found on Sunday by an Oklahoma tourist.

"This is a heartbreaking case," Shea said.

While the cause of death of the baby is still officially open, the New York Daily News reported that police suspect the father of murdering the infant in his Bronx apartment. Shea said the baby was alive when Currie took him to his Bronx apartment on Saturday under a custody arrangement and died sometime before Currie left the apartment and headed for Manhattan the next day.

Video showed Currie walking toward the river and carrying the baby in a backpack he fashioned as a baby carrier. A backpack was later seen floating in the river near the boy's body. Additional charges could be filed pending the outcome of an autopsy.

Diana Campbell, of Stillwater, Oklahoma, first noticed the baby at around 4 pm on Sunday. Her husband, Monte Campbell, waded into shallow water near the Manhattan shoreline, retrieved the baby and started CPR.

"She just called me over and said there was a baby in the water," Mr Campbell said. "I called 911. At that point, I thought it was a doll." He said the baby wasn't breathing and showed no pulse.

Police officers arrived minutes later and took the baby onto the pedestrian walkway, where they continued CPR before the baby was taken to a hospital and pronounced dead. No parent or guardian was present at the scene, police said.

The boy's mother frantically called 911 at around 9 pm on Monday after Currie failed to return the baby, per their custody arrangement. They were not married. Shea said the city's children's services administration had no prior reports regarding the child or the couple. He wouldn't comment as to whether Currie had a criminal record.