Michael Phelps' impressive comeback continued on Sunday as the 18-time Olympic gold medallist set the fastest 200-metre individual medley time of the year.

The 30-year-old continued his standout performances at the United States National Championships, clocking a time of one minute, 54.75 seconds in San Antonio.

Phelps had also won the 100m and 200m butterfly finals in year-best times.

"I'm very happy where I am right now. This is a great foundation, a place where we've never really been in a long time leading up to an Olympics," he said.

"I definitely wasn't like this leading up to '12, so it’s probably been since 2007 that we've been like this."

The time was far quicker than that of Ryan Lochte, who won the 200m IM at the FINA World Championships in 1:55.81 on Thursday.

It was Phelps' ninth 200m IM national title and 56th overall.