KAZAN - The United States grabbed two gold medals with two world records at the seventh competition day of the swimming world championwships here on Saturday.

Katie Ledecky of the US poses with her gold medal after winning the women's 800m freestyle final at the Aquatics World Championships in Kazan, Russia, August 8, 2015.  [Photo/Agencies]

The 18-year-old Katie Ledecky continued her outstanding performance in Kazan as she timed eight minutes 7.39 seconds to dominate the 800m freestyle final, 3.61 seconds faster than her previous world record set in last year.

Lauren Boyle of New Zealand finished second in 8:17.65, an Oceanian record, and Jaz Carlin of Britain took bronze in 8:18.15.

Ledecky has collected golds in the 200m, 400m and 1,500m freestyle, plus anchoring the women's 4x200m freestyle relay win. She also twice lowered her own 1,500m world record in Kazan.

The United States timed 3:23.05 to win the mixed 4x100m freestyle relay title. The previous world record was held by Australia in 3:23.29. The Netherlands came second in 3:23.10, while Canada ranked third in 3:23.59. China was seventh.

China took a bronze in women's 50m butterfly as Lu Ying, runner-up of the event at the Barcelona worlds, timed a new Asian record 25.37 seconds.