Updated

New York City will not be reopening K-12 classrooms on Sept. 21 but will instead delay K-5 and K-8 schools until Sept. 29 and middle and high schools to Oct. 1 due to coronavirus risks, Mayor Bill de Blasio said Thursday.

Until then, students will continue with remote learning, which began Wednesday.

"Obviously, remote learning has begun already. ... We are doing this to make sure that all the standards we've set can be achieved," de Blasio said during a news conference. "We have to have social distancing throughout schools, cleaning constantly, face coverings on students and adults alike."

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This is not New York City's first delay. Earlier in September, de Blasio delayed reopening classrooms to Sept. 21 in a deal struck with the city's powerful unions representing teachers, staff and administrators.

Richard Carranza, chancellor of the New York City Department of Education, left, and Mayor Bill de Blasio carry bins with supplies during a news conference at New Bridges Elementary School in the Brooklyn borough of New York, Aug. 19, 2020. (Jeenah Moon/Bloomberg via Getty Images)

Richard Carranza, chancellor of the New York City Department of Education, left, and Mayor Bill de Blasio carry bins with supplies during a news conference at New Bridges Elementary School in the Brooklyn borough of New York, Aug. 19, 2020. (Jeenah Moon/Bloomberg via Getty Images)

"This is a huge undertaking," de Blasio said, adding that the school system will hire 2,000 more educators in addition to the 2,500 additional educators set to be hired.

Thursday's delay will not affect early education sites and special education, de Blasio said.

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The development comes after de Blasio emphasized for months that the city's 1.1 million public school students need schools to resume in-person instruction this fall after the coronavirus abruptly forced a thorny plunge into remote learning in March. New York City students had their last day of in-class instruction on March 13. All schools statewide were closed by March 18.

Fox News' Danielle Wallace contributed to this report.