Hagino and Shen each collect fourth golds at Asian Games

The 20-year-old from Japan blew away his rivals on the final lap to win the men's 400 metres individual medley final -- the most gruelling event in the pool -- and show why he is one of the early favourites to win gold at the 2016 Rio Olympics.

In fourth place after the penultimate leg of breaststroke, Hagino turned on the power on the final lap of freestyle, opening up a body length's lead over his rivals.

He cruised to victory in four minutes 07.75 seconds, slashing almost six seconds off the Asian Games record, and leaving the likes of Japan's reigning world champion Daiya Seto in his wash.

"My strategy was to bring the very best potential in me for the last 100m and it worked well," said Hagino, who has won a total of six medals in Incheon and has one more event to go.

"The record is not bad either."

Chinese teenage sensation Shen Duo matched Hagino's haul of four gold medals this week when she won the women's 200m freestyle final.

Fresh from winning six gold medals at last month's Youth Olympics, the 17-year-old from Changzhou, Jiangsu left her opposition dead in the water as she charged through the first lap under world record pace and then steamed to victory in 1:57.66.

Shen also won the 100m freestyle final and two relays and has a great chance of winning a fifth with the medley relay still to come although she has her sights set on bigger prizes.

"I completely shut off what is going on around me, ignore other people, external factors and just focus on the game and me," she told Reuters.

"My goal is definitely a gold medal in Rio. What I will do from now is to focus on breaking my personal records. I think it is what I need to do before I think about breaking world records."

China won four of the seven finals decided at the Munhak Aquatics Centre on Wednesday in a further demonstration of their bottomless depth of talent with long-distance star Sun Yang switching to sprints and scooping up a gold in the 4x100m freestyle final.

Jiao Liuyang, the Olympic champion in London two years ago, won the women's 200m butterfly gold while Fu Yuanhui won the 100m backstroke for her second gold of the Games.

Kazakhstan teenager Dmitriy Balandin, another potential star who surfaced at these Games, won his second gold in as many nights when he took out the 100m breaststroke, just dipping under the one minute barrier.

Joseph Schooling provided the small island state of Singapore with a rare victory over Asia's traditional swimming powerhouses when he won the men's 100m butterfly.

Schooling, who has enrolled at the University of Texas and needed permission to come back for the Games, won gold in 51.76 seconds, becoming the first Singaporean man to win an Asian Games swimming title in over three decades.

"It is a great thing for an athlete. I am honoured that I can do that for my country," he said.

"I tried to prepare for this as best as I could but nowhere close to where I should be or I will be doing for future events."