Phelps breaks 100m butterfly world record

U.S. swimmer Michael Phelps swims to set a new world record in the men's 100m butterfly event at the USA Swimming National Championships in Indianapolis, Indiana, July 9, 2009.

INDIANAPOLIS (Reuters) - Michael Phelps broke the 100 metres butterfly world record by clocking 50.22 seconds at the U.S. National championships on Thursday.

Gold medallist at the Beijing Olympics, Phelps trimmed .18 seconds off the old mark of 50.40 ending American compatriot Ian Crocker's six-year hold on the record.

Phelps previously held the 100 fly mark for one day having broken the record in the semi-finals of the 2003 world championships in Barcelona.

Crocker took the record with victory in the final the next day and has lowered it twice since -- the last time at the worlds in 2005.

Phelps now holds five individual world records -- 400 and 200 individual medley, 200 and 100 butterfly and 200 freestyle.

(Editing by Ken Ferris)