The company says that labour disruptions in South Africa and the confiscation of a parcel of diamonds by the Tanzanian government are to blame.
Petra Diamonds Mining News
Over the last nine years 66 record-breaking and other noteworthy diamonds were recovered, and 61 of those have been found within the last five years.
Company reached wage agreement with the main union at two of its mines in South Africa. Workers will return to work on Friday.
Stock closed 12.2% higher at 64.80p, after it had fallen on Tuesday to its lowest since late 2015.
The National Union of Mineworkers said on Thursday its members would go on an indefinite strike at the mine over wages, benefits.
President John Magufuli also directed the central bank to buy the precious stone to boost reserves — the latest twist in a spat with mining firms over alleged tax evasion.
Shares in the diamond miner fell for a second consecutive day after it warned that two of its South african mines had been affected by strikes.
The Africa-focused diamond miner said that would likely happen unless it solves its issues with the government of Tanzania.
Draft bill gives government first option to buy unusually large diamonds found in the country's mines, such as the world's second-biggest 1,109 carat diamond discovered by Lucara two years ago.
The diamond miner also had to halt operations at its Williamson mine as several key employees are being questioned by local authorities.
President John Magufuli has asked for a review of a local contract belonging to Petra Diamonds and ordered senior officials to resign over the outcome of a probe into the diamond and tanzanite sector.
Labour disputes earlier in the year caused delays in the building of a new plant in its Cullinan mine in South Africa.
Lucara Diamond’s Lesedi La Rona is said to face challenges other rock never do, including its multi-million-dollar price tag and a risky polishing process that can take months or years.
President John Magufuli has also ordered the mining ministry to freeze the renewal of expired permits.
The Tanzanian government submitted three bills to parliament on Thursday that would allow it to force mining and energy companies to renegotiate their contracts.
The company, which owns the Cullinan mine that has produced the two largest diamonds in the British Crown Jewels, said output and revenue will be lower than market expectations.
The target group was the the top diamond consumer in 2015, a year in which most commodities plummeted, hitting the mining industry very hard.
The miner is confident in the long term outlook for the diamond industry and it expects is to be cash flow positive in the second half of the current financial year.
The diamond will be offered for sale in Johannesburg later this month.
Output rose 16% to 3.7 million carats, which puts Petra on track to hit its long term annual target of 5 million carats in 2018, a year earlier than planned.
It was found at Petra's Cullinan mine in South Africa, which has yielded several massive gems, including the largest rough gem diamond ever discovered.
The 121.26-carat white rock is a Type II diamond "of exceptional colour and clarity," according to Petra.
Price tag makes it the most expensive fancy intense blue diamond ever sold at auction.
The 32.33-carats diamond was recovered in November from the firm’s Williamson mine in Tanzania.
The company remains upbeat and expects a better performance in the second half, driven by a recovery in diamond prices.