Manhattan’s luxury apartment sales continued to fall in the third quarter, but now the starter market, which had been more resilient, could be losing momentum as well.

The median sales price fell to $1.1 million, down 4.5 percent, and sales volume fell by more than 11 percent from the same period last year, according to a report from Douglas Elliman. Other real estate agencies reported similar declines in sales volume and price.

That the top of the market remains soft is not surprising — a glut of new condo construction and a lack of urgency from mostly all-cash high-end buyers have hobbled luxury sales for several quarters.

But a sharp increase in inventory of studio and one-bedroom apartments suggests a slowdown of the broader market, said Jonathan Miller, the real estate appraiser who prepared the Elliman report. There was a 21 percent jump in the number of one-bedroom apartments for sale, compared to the same period last year — the most of any category — followed by a 15.5 percent increase in the number of studios on the market.