Two physicians caring for Hamlin said he was "demonstrating signs of good neurological recovery" and was able to communicate in writing.
He remains on a ventilator in the intensive care unit at University of Cincinnati Medical Center to assist his breathing.
The physicians said Hamlin had asked who won the game between the Bills and the Bengals. The response: "Damar, you won - you won the game of life," Dr. Timothy Pritts said.
That his first question was about the outcome of the game showed, "it's not only the that lights are on - he's home," Pritts said.
"It's been a long and difficult road for the last three days," said Dr. William Knight.
"He has been very sick and has made a fairly remarkable recovery," Knight said, adding that Hamlin has shown good signs of neurological and individual organ recovery .
The next milestone, doctors said, was getting Hamlin breathing completely on his own.
They said it was too soon to say whether the hit he took on the field or a pre-existing condition caused Hamlin to go into cardiac arrest.
Asked whether there was a possibility of him playing professional football again, Knight told reporters: "It's entirely too early to have that conversation."
Knight said Hamlin was still critically ill and remained in the ICU, adding that the focus was on getting him off the ventilator "and on the road to recovery."
"Per the physicians caring for Damar Hamlin at the University of Cincinnati Medical Center, Damar has shown remarkable improvement over the past 24 hours," the Bills said on their official Twitter account. "While still critically ill, he has demonstrated that he appears to be neurologically intact.
"His lungs continue to heal and he is making steady progress."
During the first quarter of the Bills' penultimate regular season game against the Bengals, Hamlin got to his feet after making a tackle and then collapsed.
After having his heartbeat restored on the field, Hamlin was transported to the University of Cincinnati Medical Center where he has remained in intensive care.
Fans, athletes, celebrities and politicians, including U.S. President Joe Biden, have all offered Hamlin their prayers and support.
Famed Niagara Falls - both the American Falls and Canadian Horseshoe Falls - were illuminated in Bills blue on Tuesday as a show of support for Hamlin, the Bills and nearby city of Buffalo.
The NFL has not yet made decision on whether to replay the Bills and Bengals game.
The postponed game, if played, would have playoff implications for both the Bills and Bengals, who are battling with the Kansas City Chiefs for the top seed in the American Football Conference, which comes with a first-round playoff bye.