By Holly Yan and AnneClaire Stapleton CNN

(CNN) -- An Orlando police officer searching for a murder suspect was gunned down Monday, and a sheriff's deputy looking for her killer died shortly later.

"To lose two law enforcement officers on this Law Enforcement Officer Appreciation Day is indeed a tragedy," Orange County Sheriff Jerry Demings said.

Orlando police Master Sgt. Debra Clayton, a 17-year veteran and mother of two, died Monday morning, Orlando Police Chief John Mina said.

The Orlando Police Department tweeted a video of Clayton's flag-draped casket as it was wheeled away from a hospital.

The chief said Clayton was trying to contact a murder suspect at a Walmart at 7:17 a.m. Two minutes later, police received a call of an officer shot.

Witness James Herman told CNN affiliate WFTV the gunman was wearing a security uniform.

"He walked by me, had a security vest and everything," Herman said. "I was walking down the sidewalk, right past the officer, and I heard her tell him to stop, or whatever, and he shot her. He shot her down."

Herman said the man continued shooting behind him as he was running from the scene.

Mina identified the suspect as Markeith Loyd, who is also wanted for the killing of a pregnant woman in December. A reward of up to $60,000 is offered for information leading to Loyd's arrest.

Sheriff's deputy killed

Authorities across Orange County scrambled to find Loyd. During the manhunt, a sheriff's deputy was killed in a crash, Demings said.

"Not only did we lose an Orlando police officer today, we lost an Orange County deputy sheriff as well who was traveling on his motorcycle," the sheriff said.

"A motorist turned in front of him. Based on eyewitness testimony, he had a green light, he was not traveling at any (high) rate of speed."

The deputy's name has not been released pending notification of relatives.

A dangerous pursuit

Demings said several law enforcement officers have been injured searching for Loyd.

At one point during the manhunt, an Orange County sheriff's captain saw a vehicle that was believed to belong to the suspect and made a U-turn, Demings said.

The suspect fired at the captain. The captain was not seriously injured, but authorities are now pursuing an attempted murder charge against the suspect.

As hundreds of law enforcement officers searched for the killer, several Orange County schools went on lockdown.

A hero who went above and beyond

While the manhunt continues, Mina said his department is grieving the death of a "hero."

"I've known Debra for 17 years. She was extremely committed to our youth and the community. She did so many different projects in the community. She organized several marches against violence by herself," the police chief said.

"Debra Clayton is a hero, and she gave her life protecting the community that she loved."

The sheriff said his department is also mourning the death of its deputy. But with an "armed and extremely dangerous" killer on the loose, there is little time to grieve.

"While we're processing our own emotional feelings, we still have a job to do," Demings said.

A deadly first for 2017

Clayton's death marks the first firearm-related fatality of a law enforcement officer in the US in 2017, said Steve Groeninger of the National Law Enforcement Officers Memorial Fund.

On Saturday, North Las Vegas police Det. Chad Parque was killed in a traffic crash.

The deaths of Clayton and the unidentified Orange County sheriff's deputy mark the second and third on-duty law enforcement officer deaths of 2017.

Groeninger said 2016 saw 136 law enforcement deaths, including 65 from firearms.

CNN's Kate Conerly contributed to this report.

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