LONDON, United Kingdom — Petra Diamonds Ltd. sank the most in almost two months in London after saying annual sales would be short of market expectations on a dearth of large gems at its main mine.

Petra dropped as much as 10 percent, the steepest intraday slide since April 16, and was at 153.9 pence by 8:14 a.m. in London.

It recovered a “lower incidence of high-quality stones and higher volumes of smaller diamonds” in South Africa, Petra said in a statement Friday. It expects annual sales of $430 million, compared with an average analyst estimate of $447.3 million. Petra retained its output target of 3.2 million carats.

By: Thomas Biesheuvel; editors: Will Kennedy, Tony Barrett and Ana Monteiro.