(Bloomberg) -- Petra Diamonds Ltd.’s chief joined other mining executives in warning that it’s still too early to tell if the industry’s rebound from the worst year since the financial crisis will last.

“Prices are up, the market definitely has a positive feel about it,” Johan Dippenaar, Petra’s chief executive officer, said in a phone interview on Tuesday. “It’s a volatile world and we’ve all learned the lesson to be a bit more cautious and not get pulled into exuberant thinking.”

After China’s slowdown and an industrywide credit crunch pushed prices down 18 percent last year, the biggest producers -- De Beers and Russia’s Alrosa PJSC -- responded by choking off supply. While that led to some stone shortages and a 3.7 percent price increase in the first quarter, De Beers and miners including Gem Diamonds Ltd. have said that it’s too early to say if the recovery will continue.

The first three or four months of the year are traditionally the busiest in the diamond industry as manufacturers and retailers rebuild inventories after the holiday season, which is a key sales period for jewelry. Dippenaar said it may take until early next year for a clear indication of the strength of the recovery.

Sales have started to increase amid renewed optimism. De Beers, the biggest producer by value, expanded sales at its last three offerings, while Alrosa’s first-quarter diamond sales surged 70 percent as it drew down stockpiles built up last year.

Earlier Tuesday, Petra reported a 26 percent jump in third-quarter production to 995,905 carats and said revenue advanced 25 percent to $120.5 million.

The Johannesburg-based company increased its full-year guidance to as much as 3.65 million carats from a earlier outlook of 3.3 million to 3.4 million carats. Petra also agreed with its lenders to improve covenant measurements and it expand its production further.

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