Swimming: Lauren Boyle storms to 1500m silver

United States' gold medal winner Katie Ledecky is flanked by New Zealand's silver medal winner Lauren Boyle, left, and Hungary's bronze medal winner Boglarka Kapas. Photo / AP.

A stunning performance by Lauren Boyle to win a silver medal ensured she became New Zealand's most successful swimmer at a world championships in Kazan, Russia today.

Boyle took second place behind American star Katie Ledecky in the 1500m freestyle final.

That takes to four the number of world championship medals the Aucklander has won after nailing three at the worlds in 2013, and one beyond the three she shared with double Olympic champion Danyon Loader.

Ledecky beat her own world record set in the heats a day earlier, clocking 15min 25.48s, while Boyle clobbered her national record in touching in 15:40.14 taking nearly five seconds off her old mark from two years ago.

It is only the ninth medal New Zealand has won at the world championships since 1978, when current coach Gary Hurring won the country's first.

Boyle joked about her distance from winner Ledecky, but was delighted with her time.

"Honestly that is the thing I am most proud of," Boyle said. "I think for me improving my time to be better than I have been in the past is the most positive thing and I am so happy to go with a personal best time. That is really exciting."

It sparked a night to savour for New Zealand swimming with Glenn Snyders qualifying for the final of the 50m breaststroke early tomorrow.

Boyle, 27, who had finished fourth in her heat, started aggressively, sat fourth, then went past Australian Jessica Ashwood on the third lap, and 2011 champion Lotte Friis of Denmark at the 700m mark.

Her relentless pace meant a deviation of just 0.3s from her fastest to slowest lap, apart from the opening 50m.

"I didn't really know what to expect when I was going into race mode," Boyle said.

''I knew that if I wanted to have any chance I had to go out with a really fast pace. And I think I got into a pretty good rhythm."

Boyle now had two days break before her final event the 800m.

''Definitely it should be good. You never quite know what will happen but I am really happy with that swim tonight and it shows I have some really good fitness."

Snyders made a hesitant start to his semifinal but fought through the field superbly in the final 15m to touch in fourth place, and sixth fastest overall. His 27.17s is his second fastest time ever, and took his heat time down by .06s.

The Los Angeles-based swimmer has a chance to grab his national record of 27.06s in the final, in an event in which two world records were set today, firstly by South African Cameron van den Burgh, in Snyders heat, then Britain's Adam Peaty, with a 26.42s in the semifinals.

In the morning heats Tauranga's Nathan Capp set a New Zealand record in heats of the men's 800m freestyle. Capp, 22, was fifth in his heat in 7:57.61 to break his own national mark.

His time was the 20th fastest and while he has missed out on qualifying, Capp has improved his world ranking by more than 30 places.

Waikato teenager Bradlee Ashby made his world championship debut to clock 2:04.31 to be 33rd ranked in heats of the 200m butterfly. The 19 year old has improved his world ranking after coming into the championships outside the world's top 50.