'Race against time': Search for missing firefighters off coast of Florida remains rescue operation Firefighters Justin Walker and Brian McCluney were reported missing on Friday.

A flotilla of volunteers answered the call on Tuesday to join the search off the Florida coast for two firefighters who failed to return from a fishing trip on Friday.

As the search for Jacksonville, Florida, Firefighter Brian McCluney and Fairfax, Virginia, Firefighter Justin Walker stretched into its fifth day on Tuesday, search-and-rescue crews clung to hope of finding the two men alive but conceded they are in a "race against time."

Search crews focused on an area of ocean where a civilian found a bag belonging to McCluney on Monday.

U.S. Coast Guard Capt. Mark Vlaun declared at a news conference Tuesday that the search mission has not changed.

"We remain optimistic, but guardedly so. At this point it is 100% still a rescue operation," Vlaun said.

More than 200 people, including members of the U.S. Coast Guard, Navy and local law enforcement, were out combing the ocean in boats and aircraft.

For the second consecutive day, Jacksonville Fire Chief Keith Powers sent out word for volunteers with boats that have the fuel capacity and capability to safely travel at least 60 miles offshore.

He said that on Wednesday the search would shift further north and asked for volunteer boaters from Savannah and Brunswick, Georgia, to join the rescue effort.

"I would say the next 24 hours are absolutely critical," Vlaun said on Wednesday afternoon. "I can't put it any clearer that we are absolutely in a race against time at this point."

He said searchers found a top to a cooler on Wednesday in the general vicinity McCluney's bag was discovered floating on the surface of the ocean. He said "we assume" the cooler top came from the boat McCluney and Walker were on.

Vlaun said another big challenge is the strong gulf current moving north and taking any new clues with it.

"Without additional clues, the area becomes vast," Vlaun said.

On Tuesday, more than 75 boats were deployed, nearly doubling the number from Monday, to search an area about 50 nautical miles off the coast of St. Augustine, where McCluney's fishing tackle bag was located, officials said. Eleven airplanes were also involved in the search on Tuesday.

We remain optimistic, but guardedly so. At this point it is 100% still a rescue operation

McCluney's wife, Stephanie, confirmed in a Facebook post that she identified the bag recovered from the ocean as belonging to her husband.

"I wholeheartedly believe this is a bread crumb they [threw] overboard to say, 'We are here, come find us,'" Stephanie McCluney said in her Facebook post on Monday night, which included a photo of the bag.

Coast Guard officials said the search, using boats and military aircraft, have covered more than 50,000 square miles of ocean since it began Friday night. Crews searched 13,000 square miles on Tuesday alone, Vlaun said.

McCluney and Walker were last seen on Friday launching a 22-foot fishing boat at Port Canaveral, which is near the Kennedy Space Center, U.S. Coast Guard officials said.

One of the main reasons McCluney and Walker were taking the fishing boat out for the day was to honor Brian McCluney's recently-departed father, Stephanie McCluney said.

"[Brian] wanted to get those lines wet one more time. You know, one big final hurrah for his dad and it was just supposed to be one great day in his honor … he was excited to get out there on the water," said Stephanie McCluney.

When the men failed to return to shore by 8 p.m. on Friday, their family members reported them missing.

About 50 firefighters from the Jacksonville Fire and Rescue Department joined the Coast Guard in searching for the lost firefighters, combing the waters between Daytona Beach and Vilano in 11 boats over the weekend.

When asked on Tuesday how much longer the search will continue, Vlaun said, “ultimately, that’s a decision that will fall to me and I can only tell you that for today we’re continuing to search and we’re searching heavily based on what we learned today."

"Each day we effectively have to take a look at what did we find the day before ... and do we still have a reasonable chance for success," Vlaun said. "For today, that answer is yes."