UPDATE 1-New York City delays in-person learning at public schools for a second time

(Adds details of delay, quote from mayor, background)

NEW YORK, Sept 17 (Reuters) - New York City Mayor Bill de Blasio delayed the start of in-person learning at public schools for a second time for most students on Thursday as the city grapples to safely reopen amid the coronavirus pandemic.

While virtual lessons via the internet are already underway, in-person learning had previously been delayed to Monday, Sept. 21, for those students who opted in.

Now, only pre-kindergarten children and students with special learning needs will start on Monday, the mayor said at a news conference. Elementary school students will begin Tuesday, Sept. 29. Middle school and high school students will start Oct. 1.

"This is a huge undertaking," said de Blasio, who oversees the largest school district in the United States, serving more than 1.1 million children. "It is difficult. It's challenging."

De Blasio said a total of 4,500 additional educators have been hired. (Reporting by Jonathan Allen and Maria Caspani in New York; Editing by Bill Berkrot)