Manny Pacquiao says he is training like a 20-year-old to break a losing streak and restablish his reputation as one of the world's best boxers.

The Filipino said on Thursday his fight against American Brandon Rios in the Chinese territory of Macau next month would be "a good window" to promote boxing in China, and he felt honoured to take part in the landmark bout.

"This training camp, I believe, is one of the longest preparations in my boxing career. I trained early because I want to prove that I can still fight in the top tier of boxing," he told reporters in his home town of General Santos in the southern Philippines.

"This time my preparation is more serious, more focused. My mind is like when I was 20 years old."

A former champion in an unprecedented eight weight divisions, Pacquiao, who turns 35 in December, is seeking to come back from two consecutive defeats that have led supporters to ask if he should hang up his gloves.

He lost a controversial split decision to American Timothy Bradley in June last year, then suffered a sixth-round knockout to Mexican rival Juan Manuel Marquez six months later.

Pacquiao said he had come to terms with his defeat to Marquez, reasoning that losing was inevitable during a long sporting career.

"I don't think I had a mistake in that fight. If you look back, I had 100 percent conditioning, aggressiveness. That is part of boxing. I accept 100 percent what happened in the last fight," he said.

After doing light training earlier, Pacquiao formally opened his training camp in General Santos last month.

His training to meet Rios, for the vacant WBO welterweight title, has largely been behind closed doors.This is in contrast to many of his previous training camps, where journalists, celebrities and other guests have dropped by to pose with the boxer.

Critics have previously questioned whether Pacquiao's diminishing prowess in the ring was because he had become distracted by his many other endeavours.

His boxing fame helped him to launch a successful political career in the Philippines, and he is now a second-term congressman with ambitions of eventually becoming president.

Pacquiao, who through the peak of his career fought almost exclusively in the United States, appeared excited at the prospect of raising the sport's profile in the world's most populous nation.

"This is a good window for the people of China to have the opportunity to watch the big fight live. This is also a good window to promote boxing in China," he said.