The average sales price for an apartment in Manhattan reached an all-time peak of $1,773,523 in the first quarter, up 15 percent from the fourth quarter and 31 percent from a year earlier, according to a report from Douglas Elliman Real Estate and Miller Samuel.

The average price per square foot hit $1,363, up 16 percent from the fourth quarter and 24 percent from a year earlier.

The number of sales totaled 3,307, up just 0.3 percent from the fourth quarter, but up a whopping 35 percent from a year earlier.

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The apartment listing inventory jumped 19 percent from the fourth quarter, to 4,968, though it was up only 0.2 percent from a year earlier.

Inventories of apartments priced at $10 million and up now stand at a "fairly typical" level of about two years, Jonathan Miller, CEO of appraisal firm Miller Samuel, told CNBC.

But he is worried about overbuilding at the high end.

"What's different about this building boom is that they're building larger, more expensive units," Miller said. "The concern is, are we building too much? Is the demand there?"

Brokers expect prices to continue rising, The New York Times reports.

"You won’t have 18 percent price jumps every month. That’s not sustainable," Dottie Herman, CEO of Douglas Elliman, told the paper. But she expects prices to return to their 2008 peaks by mid-year and then climb a bit higher.

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