(Reuters) - A mother was taken into custody on Monday after she locked herself and her toddler son in a bathroom in a New York City restaurant and the 1-year-old was later pronounced dead after workers found him unresponsive, police said.

The 35-year-old woman entered the bathroom with her child at 5 Boro Burger in Manhattan, New York Police Department Sergeant Brendan Ryan said.

After the woman spent a "large quantity of time" locked inside, workers concerned over her well-being gained access with a key and found her 1-year-old son unresponsive and foaming at the mouth, Ryan said.

The child was pronounced dead when he arrived at a hospital, Ryan said. The 35-year-old woman was in police custody and being questioned.

Police were also investigating unconfirmed witness reports that the mother said: "I put my hand over his month to put him to sleep."

(Reporting by Eric M. Johnson in Seattle; Editing by Eric Beech)