Buffalo Bills safety Damar Hamlin had to be resuscitated twice after suffering a cardiac arrest on the field but seems to be “trending upwards in a positive way”, his uncle says.

Hamlin has been in a critical condition in hospital following the on-field incident during Monday’s NFL game against the Cincinnati Bengals.

The 24-year-old had CPR on the field after colliding with Bengals wide receiver Tee Higgins before being taken to the University of Cincinnati Medical Centre.

“His heart had went out, so they had to resuscitate him twice,” Hamlin’s uncle Dorrian Glenn told broadcaster CNN outside the hospital.

“They resuscitated him on the field before they brought him to the hospital and then they resuscitated him a second time when they got him to the hospital.

“We are just taking it day by day. It seems like he’s trending upwards in a positive way.”

Hamlin was reported to be on a ventilator while sedated to help with his breathing.

Bills players and staff were seen praying together on the field as an ambulance took Hamlin to hospital.

His teammates were given a standing ovation by fans, with the game postponed following the incident.

Higgins offered his “prayers and thoughts” to Hamlin and his family and added on Twitter: “I’m praying that you pull through bro. Love”.

An NFL update confirmed the fixture will not be finished this week but added that the Bills’ clash against New England Patriots on Sunday (Monday AEDT) is still scheduled to go ahead.

“The NFL has made no decision regarding the possible resumption of the game at a later date,” the league said in a statement.

There was an outpouring of emotion across the United States in response to the incident, with fans gathering outside the University of Cincinnati Medical Centre to hold candlelit vigils for Hamlin.

His family in a statement expressed their “sincere gratitude for the love and support shown to Damar during this challenging time”.

“We are deeply moved by the prayers, kind words and donations from fans around the country,” they said.

The incident sparked an astonishing surge in support for a charitable campaign set up by Hamlin two years ago to purchase toys for children in need.

Donations to the Chasing M’s Foundation Community Toy Drive had reached nearly $US6 million ($8.7 million) by late Wednesday (AEDT).