NEW YORK (NYTIMES) - Citing high community transmission and rising hospitalisations from a fifth wave of coronavirus cases, New York City health officials Monday (May 16) strongly recommended that all individuals wear medical-grade masks in offices, grocery stores and other public indoor settings citywide.

The new recommendations, issued in a health advisory by the city health commissioner, came as the city approached the orange, or "high" alert level for Covid-19, a benchmark it expects to hit in the coming days.

The new advisory also called on those who are at increased risk for severe illness, including unvaccinated children younger than 5 and people older than 65, to avoid non-essential indoor gatherings and crowded settings.

The recommendations are not mandates, however. Mayor Eric Adams, who rolled back school masking regulations and vaccination checks at restaurants and theatres months ago, has not signalled a willingness to return to mandates, though he has said he is watching the situation closely.

"We are not at the point of mandating masks," Mr Adams said Monday, adding that city hospitals were not overwhelmed and that there were new tools, like antivirals, to deal with the virus.

"We are not at the point of doing anything other than urging New Yorkers, while you are indoors in large settings, social settings, wear your masks.

"If there comes a time that our hospitals are in a state of emergency, or we're trending that way, and my doctors that run the hospitals tell me this is what we need to do, I'm going to listen to them," he added.

The mayor's own health policy, published in March this year, recommends that he institute a mask mandate for all public indoor settings, once the city hits a high level of coronavirus transmission.

However, he can choose not to follow that recommendation, and in the past has emphasised that he can use his discretion while setting health policy. When the city entered the medium alert level, he did not restore an indoor mask mandate in schools nor a policy requiring proof of vaccination for indoor dining.

The new masking recommendations come as New York City offices and businesses strain to return to something resembling their pre-Covid normal. Most city offices stopped requiring masks months ago, and masks inside stores are now the exception rather than the rule.

But the new health advisory specifically mentions offices - and meeting rooms, restrooms, elevators and hallways - as locations where people should now wear masks, preferably medical-grade, even if they are vaccinated.

It remains to be seen if offices will reinstate mask rules en masse.

Mr Jonathan Freedman, a spokesperson for Jefferies, an investment bank based in midtown Manhattan, said that his firm will continue requiring workers to mask up in meeting rooms and hallways, a policy it never dropped even as other offices did.

"We were probably an outlier in that we never told people to stop masking in common areas," he said.

After a six-week lull following the enormous Omicron wave in December and January, new confirmed cases have been steadily rising in New York City since March.

The increase is being propelled by a rapidly spreading Omicron subvariant, BA2121, that was identified in April by state health officials and is now a growing share of cases around the country.

A majority of New York counties are already at the Centres for Disease Control and Prevention's orange, or high alert level.

A high alert level is triggered when virus cases reach at least 200 per 100,000 residents per week, and new hospital admissions reach 10 patients per 100,000 residents per week, a sign of rising strain on the hospital system.

As of Monday, New York City was reporting hospital admission levels just slightly below that threshold, and 291 cases per 100,000 residents per week.

New York City also has a fourth virus level, very high, which would only be triggered if hospitals reach 90 per cent capacity.

While hospitalisations remain far below where they were in January, hospitals in upstate New York, where BA2121 has been spreading for months, have been reporting strain as hospital workers go out sick with virus infections, worsening existing staff shortages. But the percentage of virus patients in intensive care has remained relatively low.

As of Sunday, an average of 22 people were dying statewide each day, according to a New York Times database - an increase of 27 per cent over the past two weeks, but still a fraction of the more than 200 people who were dying each day in late January.

In New York City, the public hospital system said in a statement Monday that the volume of patients with Covid-19 remained manageable and that the system was stable.

As of Sunday there were 714 patients hospitalised with Covid in New York City, according to state data. At the peak of the omicron wave in January, there were 6,500 patients hospitalised. In April 2020, at the peak of the first wave, there were 18,000 patients hospitalised in the city.

Northwell Health, the state's largest health system, said Monday that it was treating 300 patients infected with the virus across its 21 hospitals, more than half of whom had been admitted for other reasons and tested positive once they arrived, a trend reported statewide.

By contrast, on Jan 11, at the peak of the first Omicron wave, Northwell had 1,730 patients infected with the virus hospitalised, said Mr Joe Kemp, a spokesperson.

Still, Dr David Battinelli, Northwell's physician-in-chief, said that his system was under some stress because of increased virus cases sidelining workers, and the added effort required to isolate and treat Covid-19 patients in the hospital.

"My opinion is we better do something now before the numbers really go up," he said. "Masking is the most contentious, but it is the most effective of the measures."