The seawall and edge of the concrete walkway, located at East 89th Street in Carl Schurz Park, deteriorated and fell thanks to Friday's downpour, the city's Parks Department said.
The collapse took the esplanade's iron fence with it, fully exposing the walkway to the river.
The Parks Department is going to expedite reconstruction of the Esplanade, but a timeline is still being determined, officials said.
"Parks is working to immediately address the safety issue at Carl Schurz Park," said Crystal Howard, a spokeswoman for the agency. "We have placed barriers around the site, and Parks personnel are posted in the park around the clock to ensure safety."
The affected area is included in the agency's first phase of its $15 million redevelopment project, which will rework the stretch's drainage and replace benches and concrete pavers.
This isn't the first time part of the Esplanade has fallen into the river.
There have been numerous sinkholes over the years, including a 20-by-10-foot hole between 89th and 96th streets that was recently patched up.