New York City, once the epicenter of the coronavirus pandemic in the United States, will enter its next phase of reopening on Monday, with as many as 300,000 employees expected to return to their jobs as outdoor dining, in-store shopping and office work resume, Mayor Bill de Blasio said on Thursday.

The move will put the city one step further on its path to economic recovery from a devastating virus that killed more than 21,000 residents and triggered one of the strictest shutdowns in the United States.

“I’m very comfortable now saying that we will start Phase 2 on Monday,’’ Mr. de Blasio told reporters at his daily briefing.

Gov. Andrew M. Cuomo said later on Thursday that the state would not make its final decision on easing more restrictions until Friday, but was still advising businesses to prepare for it, given recent testing and hospital data.

“My advice to New York City businesses: plan to reopen Monday in Phase 2,” the governor said.

Mr. de Blasio’s announcement comes as other states that moved more swiftly to reopen have seen spikes in new infections. Arizona, Florida, Nevada, Oregon and Texas all reported their largest one-day increases in new cases this week.

Yet New York has shown a steep decline in new cases since the virus peaked in April, when there were more than 10,000 new cases reported on several days. On Thursday, the state reported another 618 cases, or about 0.90 percent of all tests processed the day before — the lowest rate since the beginning of the outbreak, according to the governor.

Under the state’s reopening plan, outdoor dining, some in-store shopping, hair salons, barbershops, real estate firms and offices in the city would be allowed to open up in the second phase, with social distancing and restrictions on capacity. Playgrounds will also reopen during Phase 2, Mr. de Blasio said.

The newly reopened businesses will likely offer a jolt of energy to New York City’s streets, which had been eerily quiet as the state’s lockdown orders shuttered businesses and kept residents at home.

Restaurant owners, who have seen business plummet during the pandemic, have been particularly worried that even as the city reopened, regulations requiring them to limit capacity and put distance between their tables would make it hard for them to make ends meet.

Many restaurants and bars in New York City, especially in Manhattan, do not have available outdoor space, and owners have for weeks pressed lawmakers to expand their ability to serve customers outdoors as the city reopened.

As the city first began easing restrictions earlier this month, a kind of informal outdoor dining emerged, with large groups eating and drinking on streets outside businesses that were open for takeout.

On Thursday, Mr. de Blasio said that restaurants in the city would be able to place seating in curbside parking areas and on sidewalks adjacent to their restaurants, even if those establishments had never provided outdoor seating before.

He also announced that beginning in July, the city would allow restaurant seating on the 43 miles of streets that it had closed as part of its Open Streets program. Under the program, roads were closed to vehicle traffic in an effort to provide more outdoor space to residents and prevent crowding at city parks.

“Outdoor dining is the way forward,” Mr. de Blasio said.

The mayor predicted that the expansion of outdoor dining could prevent 5,000 of the city’s restaurants from closing and avoid the loss of 45,000 jobs. For restaurants that do not already have outdoor seating permits, an expedited application process will begin on Friday, officials said.

Ted Pavlakos, a manager at Hudson Clearwater in the West Village, which has a popular patio as well as sidewalk seating, said the restaurant was “absolutely ready to open on Monday for outdoor seating.”

In recent days, he said, customers have been stopping by the restaurant in-person and calling to see when the patio would reopen. Many, he added, seem to be “itching to come back.”

“We can’t wait to have people back in,” Mr. Pavlakos said. “I’m really curious to see the general vibe will be.”

Still, not all New York business owners were excited by the prospect of entering Phase 2.

Lexi Beach, the owner of Astoria Bookshop, an independent bookstore that has been offering curbside pickup, said she was concerned the city was “moving too quickly” and that she doubted that she would allow customers into her store on Monday.

“It’s not that we want to be operating slowly and with a bottleneck of pickups by appointment,” she said. “It’s that this is the way that we can do it to minimize risk. I don’t even want to say it’s the ‘safe’ way to do it.”

Ms. Beach also expressed deep frustration about what she said was poor communication by the city and state about what the phases actually entail.

She noted that customers have been showing up at her store during Phase 1, under the false impression that they can come inside and browse. And as a business owner, she said she has not received any guidance on how to ensure she maintains a steady supply of disinfectants and other cleaning materials required to keep customers and employees safe.

“It’s very complicated,” she said, “and I am not happy that we are moving into Phase 2 so quickly.”

Mr. de Blasio and Mr. Cuomo have also repeatedly emphasized the need for caution as the city prepared for Phase 2, with both suggesting they could still delay reopening if the test results over the weekend showed a spike in new cases.

Mr. Cuomo, pointing to issues in other states, urged New Yorkers to continue social distancing and wearing masks in order to prevent a second wave of infections.

Earlier this week, the governor threatened to reinstate closures in the city after a number of photos and videos spread online of people flouting social-distancing rules and congregating outside Manhattan bars.

On Thursday, as the city prepared to expand outdoor dining, Mr. Cuomo said he would sign an executive order allowing the state to immediately suspend the liquor license of a business or shut it down if it was not complying with reopening guidelines. He also said he would sign another order that gave bars the responsibility to limit the number of people gathered outside their establishments.

New York City was the last region of the state to begin the reopening process, on June 8. Its suburbs entered Phase 2 this week, and the rest of the state has already moved on to Phase 3, which allows indoor dining at restaurants and personal-care services.

The very factors that made the city an epicenter of the pandemic — its density, tourism and dependence on mass transit — complicated efforts to return to a state of normalcy.

Among major concerns was the city’s public transportation system, which relies on heavily packed, enclosed spaces to ferry millions of people across New York. The next phase of the reopening was expected to send more riders back onto public transit, especially the subway, where ridership plunged by more than 90 percent as the pandemic hit.

The Metropolitan Transportation Authority, which runs the city’s subway, buses and two commuter rails, said this month that it expects just over two million daily riders will use public transportation in Phase 2.

In anticipation, transit officials are urging riders returning to the system to wear face masks, use hand sanitizer, avoid rush hour and seek out less crowded train cars where possible. Subway workers have been cleaning the system nightly and have taken steps to encourage social distancing in stations and on trains.

Reporting was contributed by Luis Ferré-Sadurní, Christina Goldbaum, Dagny Salas and Matt Stevens.