Mai Nakamura broke the world record in the women's 50 meters backstroke while Masami Tanaka completed the Japan Swimming Championships in "perfect" style on Sunday, clocking national records in all seven of her breaststroke races.

Nakamura bettered the previous world record, set by Spain's Nina Zivanevskaya at the Spanish Championships on April 8, by 0.02 of a second, finishing in 28.67.

"When I looked at my time in the first half of my 100-meter race, I thought I could make it," Nakamura said.

Tanaka touched in 2 minutes and 24.12 in the final of the 200-meter breaststroke, cutting her old mark, which she set Saturday, by 0.15 of a second to win the event for the fifth time in a row.

Tanaka's 200-meter record is second only to the world record of 2:23.64 of South African Penny Heyns, slower by 0.48 of a second.

"This is all I could do with my ability at the moment," said Tanaka. "I thought the world record was something that I wouldn't be able to make. But after setting the record today, I've started thinking I may be able to make it and I've got a stronger self-belief and a feeling that I want to beat her more than before."

The 21-year-old Hokkaido native set a new national record every time she swam -- in the heats, semifinals and finals of both the 100-meter and 200-meter events as well as in Sunday morning's 50-meter breaststroke time trial. She sped to a time of 31.75 seconds in the 50 meters.

Nakamura finished third in the 200-meter backstroke final, which was won by defending champion Miki Nakao in 2:10.73.

Sumika Minamoto timed 25.29 seconds for a new Japanese record en route to victory in the women's 50-meter freestyle, and Sachiko Yamada defended her women's 400-meter freestyle title with a time of 4:09.80, also a domestic record.

The annual competition served as an Olympic team selection meet. The successful members for the Japanese team will be announced on Monday by the Japan Swimming Federation.