North Korea may already have 20 nuclear warheads - double as many as previously thought, Chinese nuclear experts have warned. The pariah state may also have the capability to produce enough weapons-grade uranium to double its arsenal by next year, The Wall Street Journal has reported. Chinese estimates of Pyongyang's nuclear production, relayed to US nuclear specialists, exceed most previous US forecasts of between 10 to 16 bombs, said the report, which cited people briefed on the matter. Scroll down for video . A North Korean vehicle carrying a missile passes by during a mass military parade in Pyongyang's Kim Il Sung Square. The pariah state may have as many as 20 nuclear warheads, it has now been suggested . North Korean leader Kim Jong Un addresses Korean People's Army pilots in an undated photo released by the state news agency earlier this month. Under the Kim dynasty North Korea has long used nuclear weapons as a bargaining chip in international relations . Experts at the US-Korea Institute at Johns Hopkins University's School of Advanced International Studies earlier this year presented three scenarios for North Korea's nuclear capability, predicting its stockpile of weapons could grow to 50 or even 100 within five years. North Korea has conducted three nuclear detonations, the most recent in February 2013. Asked about the report at a regular press briefing yesterday, China's Foreign Ministry spokesman Hong Lei said he 'did not have knowledge of the specific situation'. 'We must persevere with denuclearisation on the Korean peninsula, persevere in safeguarding peace and stability, and persevere in resolving the relevant issue through dialogue,' Hong said. Earlier this month, US Admiral William Gortney, commander of the US Northern Command and North American Aerospace Defense Command, said the US military believes North Korea has the ability to miniaturise a warhead and mount it on a ballistic missile, although there had been no tests. One such rocket is an intercontinental missile with could theoretically hit California as it is designed to carry a payload of more than 5,000 miles. Kim Jong Un (centre in black) posing with his soldiers on top of snow-covered Mount Paektu in North Korea. The country could have as many as 100 warheads within five years, it has been suggested . Stanford University professor Sigfried Hecker was allowed to visit Pyongyang in 2010 and reported seeing a large uranium-enrichment facility. The Journal quoted him as saying: 'Some eight, nine, or 10 years ago, they had the bomb but not much of a nuclear arsenal. 'I had hoped they wouldn't go in this direction, but that's what happened in the past five years. 'The more they believe they have a fully functional nuclear arsenal and deterrent, the more difficult it's going to be to walk them back from that.' North Korea carried out nuclear tests in 2006, 2009 and 2013, and has an extremely active ballistic missile development programme, although expert opinion is split on how much progress it has made, reports Agence France Presse. The Chinese estimate reflects growing concern in Beijing about the nuclear ambitions of its errant ally, and is the latest in a series of expert assessments that suggest Pyongyang is moving faster down the nuclear path than previously thought. Kim Jong Un inspecting the newly built Wonsan Baby Home and Orphanage in a photo released earlier this month. North Korea has conducted three nuclear detonations, the most recent in February 2013 . In 2012, Pyongyang demonstrated its rocket capabilities by sending a satellite into orbit, but it has yet to conduct a test that would show it had mastered the re-entry technology required for an inter-continental ballistic missile. The other key question is how close the North is to being able to miniaturise a nuclear device that could be fitted on the tip of a missile. In a white paper published in January, the South Korean defence ministry said the North had already taken its miniaturisation technology to a 'significant' level. Under the Kim dynasty, represented by current leader Kim Jong Un, North Korea has long used nuclear weapons as a bargaining chip in international relations. Last month the country's ambassador to the UK issued a chilling warning that North Korea would be prepared to use nuclear weapons. In a rare interview, Hyun Hak-bong claimed the secretive state could launch a deadly warhead 'anytime'.
Pariah state may have 20 warheads not 10 as previous US forecasts held .
Stockpile of weapons could grow to 50 or even 100 within next five years .
US military believes secretive country has ability to miniaturise warhead and mount it on ballistic missile, though there have been no such tests yet .