The US has less than half the tonnage in warships we had in 1945. But that doesn't equate to a weakening of US Naval power by any means. US warships are vastly more capable and versatile than they've ever been.
The Chinese have more commissioned vessels, but less than 3/4 of the US Navy's total tonnage of ~4.7 million tons. That equates to lots of smaller ships, still a "brown water" focus, and not yet capable of power projection across oceans. A "blue water" navy.
They may get there relatively quickly in terms of tonnage, but experience is the biggest problem and not easily learned. We have over a century on them in that regard. Then there's the geography problem. They're hemmed in by US and allied bases and assets from Japan to the Philippines. Then there's the Strait of Malacca. Major choke point. Like Russia, geography is not their friend, making blue water power projection far more difficult than it is for us.
Short answer, they may have more ships but if they've not yet learned how to operate their navy effectively, they're just building more targets. At least from the view of an old submariner. Target rich environment. 
Then again, the Brits probably said the same about us circa 1920. Back then, in addition to a possible conflict with Japan, our primary naval adversary was Great Britain. Things changed a lot between then and 1941. Where this current rivalry will go is anyone's guess.
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