New York City has stressed to the US government the "urgency" with which it needs monkeypox vaccines amid a rise in cases, its mayor said Wednesday.

America's biggest metropolis has recorded 336 infections but that is unlikely to reflect the true numbers, according to the city's department of health.

Official cases rose from 267 on Tuesday, up from 223 the day before.

Anyone can get and spread monkeypox but many cases have been found in men who have sex with men.

The city of around nine million people is home to a large gay community and health authorities had to apologize this week after its vaccine reservation website crashed when it was overwhelmed with people trying to book appointments.

Some 1,250 slots were available but many social media users expressed frustration at being unable to book an appointment.

Mayor Eric Adams said he had had a telephone meeting with the US Department of Health and Human Services and the Centers for Disease Control and Prevention.

"We discussed the supply constraints that New York City is facing and the urgency to expand our vaccine access footprint to more people, in more neighborhoods, through more partners and providers," he said in a statement.

New York is due to receive 14,500 doses from the US government this week, adding to the nearly 7,000 it has received since June 23.

Health services are prioritizing the two-dose vaccination for gay, bisexual, or other men who have sex with men, as well as for transgenders and non-binary people.

Monkeypox is a viral illness endemic in West and Central African countries that causes symptoms such as fever and rash.

It is similar to but less severe than smallpox, but can be riskier in immune compromised people.

It is primarily spread through close contact.