As coronavirus cases increase in New York City with a current 3.09% daily positivity rate and a 2.83% seven-day rolling average, Mayor Bill deBlasio said that parents should prepare for possible school closings.

"[The positive rate] is still below 3%, so schools remain open. But that number has gotten quite close to 3% and we are making preparations as a result in case that number does exceed 3% and we have to temporarily close our schools," the mayor told WNYC on Friday.

"People should get ready … this is not something any parent wants to deal with. We should get ready. And parents should have a plan for the rest of the month of November, that’s a safe way to think about it. Have an alternative plan for beginning as early as Monday for whatever will help them get through this month if school is not open," he said.

In New York City, there have been 916 new reported cases over a seven-day average and 121 hospitalizations.

ABC News' Aaron Katersky contributed to this report.

As he has repeatedly stressed throughout the pandemic, on Friday, the World Health Organization Director General Dr. Tedros Adhanom Ghebreyesus, once again urged countries to use all tools available to combat the virus, not just wait for a vaccine.

"There is no doubt that a vaccine will be a vital tool for controlling the pandemic, and we’re encouraged by the preliminary results of clinical trials released this week," Tedros said at the closing of the WHO's World Health Assembly.

"But we have a long way to go. The world cannot put all its eggs in one basket, and neglect the many other tools at our disposal that countries like Thailand have shown are effective for bringing this virus under control," he said. "The virus itself has not changed significantly, and nor have the measures needed to stop it. We know what works. First, know your epidemic and do the basics well. Find, isolate, test and care for cases. Trace and quarantine their contacts. And second, engage and empower communities to protect themselves and others with the full range of measures: physical distance, avoiding crowds, ventilation, hand hygiene, and masks," he said.

ABC News' Kirit M. Radia contributed to this report.

For the first time since the pandemic, official travel advisories have been issued for the West Coast.

As the leftover candy stash runs low in American households across the country, several state officials and school authorities have begun citing coronavirus outbreaks related to Halloween, less than two weeks after the fall holiday.

Throughout the pandemic, social gatherings and crowded venues, juxtaposed to the highly infectious virus, have resulted in a widespread escalation of COVID-19 cases across the country. Prior to Halloween, the CDC and other health experts had repeatedly warned Americans about the risk of contracting COVID-19 during the holiday, and in particular, at indoor costume gatherings.

Despite these warnings, some people still flouted recommendations.

Although several large events made headlines, such as a gathering in Utah, which reportedly attracted thousands of costumed attendees, other smaller events in private homes and dorm rooms seemingly slipped under the radar.

And now, officials say those events may be contributing to the surging COVID-19 case numbers seen in communities across the country.

As Oregon recorded its highest daily case figure on record on Thursday, health officials said that this week's rising case numbers could be traced to Halloween-related events; specifically, several small social gatherings, as well as a party with more than 100 people in attendance.

During a press conference earlier this week, California Gov. Gavin Newsom also said officials believe the state's recent increase in cases may be tied to Halloween celebrations. And as cases rise in Vermont, which has maintained relatively low COVID-19 case numbers throughout the pandemic, some COVID-19 clusters and outbreaks have been traced back to Halloween parties.

In Missouri's St. Louis County, a Halloween party has led to at least five positive COVID-19 cases, with possibly 200 high school students exposed to COVID-19, according to local officials, and following an increase in cases, the city of St. Louis Mayor Lyda Krewson announced new restrictions Thursday on private gatherings.

In New York, Suffolk County Executive Steve Bellone tied his community's "disturbing" rise in coronavirus cases to Halloween gatherings. Another county official in Onondaga County, New York called the recent COVID-19 uptick "the Halloween surge."

Colleges have also found themselves facing the consequences of students' desire to celebrate the holiday, as COVID-19 clusters pop up on campuses. In the last week, Tulane has reported over 300 new coronavirus cases, which the college president said were the result of "poor decisions" over the Halloween weekend.

The University of Tennessee-Knoxville has also identified a COVID-19 cluster connected to an off-campus gathering on Halloween.

Although it is ultimately difficult to measure how much these gatherings are actually contributing to the exponential surge the U.S. is currently experiencing, it is clear that when mitigation efforts are not followed at celebrations, COVID-19 cases may likely follow -- a worrisome trend heading into the winter holidays.

ABC News' Arielle Mitropolous and Ali Dukakis contributed to this report.

The number of new COVID-19 cases hit another high on Thursday, as the country experiences record growth in cases, according to The COVID Tracking Project.

There were 150,526 new cases reported on Thursday, according to the data tracker. The seven-day average stands at nearly 130,000 cases, which is a dramatic 71% increase from more than two weeks ago, it found.

"Cases nationwide are trending up more quickly than at any point in the pandemic," The COVID Tracking Project said.

This week, 1 in every 378 U.S. residents tested positive for COVID-19, based on the tracker's data.

Current hospitalizations also hit a new high on Thursday, at 67,096. The death toll was 1,104.