Thousands of runners hit the streets of Brooklyn at 7 a.m. as the New York Road Runners RBC Brooklyn Half Marathon returned to full capacity for the first time in three years.

The run was marked by sadness. At the finish line, a 30-year-old runner collapsed and was pronounced dead at Coney Island Hospital of a possible cardiac arrest, the NYPD said.

The FDNY said 15 other people were sent to the hospital with injuries. 

Despite the heat and air quality alerts in effect Saturday, some runners were determined to participate in the race's return. 

“That was my first half marathon. I've never run in heat before. That felt so good. God bless New York. God bless America. It felt so good,” Emily Foley said.

Twenty-two thousand runners were expected Saturday, starting near Prospect Park and following the 13.1 mile course down Ocean Parkway to the Coney Island boardwalk where they crossed the finish line. 

“I was like, 'man I was ready to stop.' I was ready to give up but I was like, 'I’m not giving up. I’m like finish strong, finish strong,'" Patricia Almnonte, a Bronx resident, said.

Some runners said they were excited to be running this race on this particular day.

“Well today is Biggie's birthday. So I’m repping Biggie. Brooklyn all day,” Isaiah Guzman Jr., a Queens resident, said.

Others said the climate this morning made it a little tough.

“I think definitely the humidity. You know you gotta stay hydrated. Take salt tablets and just know your body slow down when you have to. Stay hydrated. And just have fun with it,” Luis Morales, a Brooklyn resident, said.