Authorities are searching for swimmers in the waters off New Jersey Thursday evening.

In Monmouth County's Belmar, emergency personnel responded to two incidents within less than an hour late Thursday afternoon, a fire department source said. 

In the first incident, rescue crews responded to the vicinity of the unguarded 9th Avenue beach around 6:30 p.m. and pulled a young girl from the ocean, according to the source. Another child was pulled from the nearby water shortly after the first rescue. 

Both swimmers, students at the borough's elementary school, were taken to Jersey Shore University Medical Center in Neptune. A young girl died, and another is in critical condition, Belmar Mayor Matt Doherty told NJ.com. Doherty said the girls are cousins and their families were notified but did not have additional information, the website reported. 

Emergency crews continued to search for another possible missing swimmer Thursday evening, bystanders said, but authorities confirmed that the search was a precaution and eventually unfounded. 

In Atlantic City, a city police department spokesperson tweeted that firefighters, beach patrol, and the United States Coast Guard were searching for two missing swimmers off in the waters off the Martin Luther King Jr. beach. 

The two teenagers reportedly went missing around 6:30 p.m. The Press of Atlantic City reported that a male swimmer attempted to rescue a female from the water. Authorities said Thursday evening that crews were working on a recovery.

The National Weather Service advised of a moderate risk of rip current development on Thursday. 

This is a developing story.