Biden addresses New York City subway shooting investigation: 'We're not letting up'

President Joe Biden addressed the New York City subway system shooting that left at least 29 injured on Tuesday while he was in Iowa as federal authorities in Washington assist New York officials in an intense manhunt for the suspect.

"To start, I'd like to say a few words about the mass shooting in New York City subway this morning, you all read and heard about," Biden began, before delivering remarks on easing gas prices. "Jill and I and my wife Jill and I are praying for those who are injured and all those touched by that trauma, and we're grateful for all the first responders who jumped into action, including civilians -- civilians who didn't hesitate to help their fellow passengers and try to shield them."

"We're going to continue to stay in close contact with New York authorities and as we learn more about the situation over the coming hours and days," he said. "We're not letting up on it until we find out, and we find the perpetrator," he said.

Biden was briefed on the shooting earlier, White House press secretary Jen Psaki tweeted, before he departed for Iowa. Senior White House staff are also in contact with New York City Mayor Adams and Police Commissioner Keechant Sewell as the situation unfolds, she said, and Biden reiterated.

En route to Des Moines, Psaki told reporters on Air Force One that she spoke with Biden aboard the plane about the ongoing situation and said the president reiterated a commitment to provide assistance to local leaders on the ground as the investigation continues.

"Anything they need, anything they want. We are here to help them and provide that to them," Psaki said.

She said Biden and New York City Mayor Eric Adams have not yet had a phone call Tuesday.

The still at-large suspect -- who police said was wearing a green vest and a hooded gray sweatshirt -- is believed to have opened fire inside at least one subway station during morning rush hour traffic. There are at least three active crime scenes in Brooklyn. Authorities said at an earlier press conference that the lone gunman put on a gas mask, deployed a smoke canister, and when the subway car filled with smoke, opened fire inside the car and on the platform.

Among those injured, according to the FDNY, 10 were shot. Five people are in critical but stable condition.

The NYPD has put out a citywide alert for a UHAUL vehicle and shared a description of the suspect with federal authorities. The shooter's motive remains unclear, police said.

Vice President Kamala Harris has received regular updates on the shooting, according to a White House official. Attorney General Merrick Garland and Department of Homeland Security Secretary Alejandro Mayorkas have also been briefed.

Senate Majority Leader Chuck Schumer of New York tweeted that he is "closely monitoring" the unfolding situation in what he called "our beloved Brooklyn."

"I'm grateful for the quick action of our first responders," he said. "To everyone in New York: Stay safe."

The shooting sparking panic across New York City comes as Adams has vowed to combat gun violence as mayor amid a recent surge in crime.

ABC News' Aaron Katersky, Josh Margolin, Alexander Mallin and Emily Shapiro contributed to this report.