Family and friends have paid tribute to boxer Lemuel Silisia who died in hospital from head injuries days after competing in a professional bout in regional New South Wales.

Described as a "brother, friend and father-to-be," Silisia, a Solomon Islander who lived and worked in Australia, died on Wednesday night, his family said.

Silisia was competing in the World Boxing Foundation Australasian Super Lightweight Title fight in Tamworth on Saturday night.

The ABC understands about 1,000 people watched the fight, which went for eight rounds.

Silisia knocked down his opponent, Adam Flood, in the third round but lost the contest on points in a fight that onlookers described as "tough and clean".

After the fight, he answered questions from the media, spoke to supporters in the crowd and posed for photos with them.

Later, family members informed his large following in Solomon Islands and his adopted home of Tamworth that the champion boxer was fighting for his life in hospital. 

NSW Police confirmed the 27-year-old was admitted to hospital on Sunday night with a head injury resulting from the bout. 

Family members reported his death on Wednesday night.

A report will be prepared for the coroner. 

In a tribute posted online, his brother Colson said after not responding to brain function testing, Lemuel was declared medically dead.

"His brave heart continued to fight until it eventually ceased beating today [Wednesday] at 5:24pm, when he was called to be with the Lord Jesus Christ," he said.  

"In this time of immense mourning and sorrow, the Silisia family kindly asks for your support and prayers. Your love, thoughts, and prayers provide solace as we navigate through the pain of this loss.

"Though our hearts ache, we hold dear the memories we shared with him, preserving his spirit in our hearts."

His family said Silisia will be brought home to Solomon Islands for a funeral service. 

The ABC has contacted the World Boxing Foundation for comment. 

Chasing 'a golden opportunity'

Silisia, who his family called "Lucky", moved to Australia in 2021 and was working in a meatworks factory as part of the Pacific Islands Labour Mobility Scheme.   

In an interview earlier this year, he said the move offered work opportunities but also enabled him to develop his boxing career.

"In the Solomons, even if you're good at sport, to be successful it depends on who you know, rather than what you know, but Australia is a big country with lots of opportunities in sport," he said.

But at the heart of his reasons for leaving his home was a deep sense of personal responsibility to his family.

Before last weekend's bout, he'd won a fight in November against opponent Simon Rendina in a technical knockout, another in April, and was undefeated heading into it. 

He was moving closer to his goal of securing a global ranking and building crucial experience in the ring.

The Solomon Islander had worked hard and built momentum before his bout at the World Boxing Foundation Australasian Super Lightweight title.

He'd been nicknamed "the Destroyer" as he clinched victories and trained hard, building a reputation throughout NSW as a tenacious fighter. 

Known also to friends as "Lems", the boxer was well-known in his adopted base of Tamworth. 

In an online post, Silisia's Tamworth-based boxing club One2 Boxing Westside said it was heartbroken. 

"The last few days we have been bedside with our beloved Lemuel, family and friends," the club said.

"Your O2B family are heartbroken and we promise your legacy will live on. Rest in peace Lems."