An 8-month-old girl became Hong Kong's second recipient of a heart donated from the Chinese mainland on Sunday, thanks to a specialized cooperation mechanism established after the first successful transplantation in 2022.

After waiting more than four months for a suitable donor, the recipient, identified under the pseudonym Whitney, underwent a 6.5-hour surgery at Hong Kong Children's Hospital that started at around 2 pm on Sunday.

Hospital officials said the operation went smoothly, and Whitney is now under close observation in intensive care. She is expected to remain in critical condition for at least 24 hours.

Due to donation regulations, authorities did not disclose details about the donor other than confirming they were from the mainland. Whitney received the heart after no other suitable recipients were found in the special administrative region.

During a Monday news conference, Whitney's father, who gave his surname as Cheung, expressed profound gratitude to the medical team and the donor's family, calling the transplant a miracle.

"This act of love and blessing will provide my daughter with the strength she needs for her ongoing recovery," he said.

Whitney suffered cardiogenic shock on Sept 14 and was placed on the local heart transplant waiting list.

Because of the rarity of donors meeting the necessary criteria, a suitable heart was not identified until Saturday, when the hospital was notified of a match.

The hospital noted that this was Whitney's third open-heart surgery, increasing the complexity and risks, including the removal of previously implanted ventricular assist devices to minimize ischemia time for the donor's heart.

On Monday, the Hong Kong Special Administrative Region government thanked the central government and mainland authorities for facilitating the transplant, which marked the second cross-border organ donation between the mainland and Hong Kong.

The first took place in December 2022, when a 4-month-old Hong Kong girl named Tsz-hei received a heart from a brain-dead mainland donor, leading to the establishment of a case-based cross-border organ transplant mechanism.

Simon Tang, director of cluster services at the Hospital Authority, said that since the 2022 transplant, authorities have worked to refine each step of the process.

Asked about the timeline for establishing a permanent cross-border transplant mechanism, Tang said it involves numerous regulations and procedures.

For now, the priority is expediting the transfer of suitable organs while adhering to legal frameworks in both regions, he said.

The latest operation followed stringent regulatory approvals and legal protocols.

Nicholson Yam, the lead consultant for the transplant at the hospital, said experts from the National Quality Control Center for Heart Transplantation procured the heart on the mainland before it was transported to Hong Kong via Shenzhen.

The delivery involved more than 100 personnel from 18 mainland agencies, including the National Health Commission, the State Council's Hong Kong and Macao Affairs Office, and various customs and public security agencies.

Hong Kong Secretary for Health Lo Chung-mau said the case demonstrated enhanced cooperation between Hong Kong and mainland authorities.

"This successful case exemplifies the strengthened collaboration in cross-border organ transplants," he said.