* Steel rebar ends 6-year losing streak
* Boosted by better demand, soaring raw material prices
* Concerns about growth, pollution cuts linger (Updating prices)
By Josephine Mason and Muyu Xu
BEIJING, Dec 30 (Reuters) - Chinese steel and iron ore prices finished the final trading session of the year under pressure amid lingering concerns about slower demand growth in the world's top commodities market, even as both markets snapped years-long losing streaks in 2016.
On Friday, investors booked profits from the gains this year and worried about the impact of a slowdown in China's economy, the world's second-largest, and more factory closures as authorities warned of another bout of toxic smog in the north of the country.
The most-active rebar contract for May delivery on the Shanghai Futures Exchange settled down 1.35 percent at 2,911 yuan ($419.04) per tonne.
Iron ore on the Dalian Commodity Exchange was down 1.8 percent at 554.5 yuan a tonne.
Snapping a six-year losing streak, rebar prices have soared more than 60 percent this year on better-than-expected spending on construction and infrastructure and soaring costs for coking coal due to government-enforced coal mine closures.
Those factors have spurred a prolonged buying spree by China's retail and institutional investors, even as regulators sought to crack down on speculation.
Earlier this month, prices hit 3,557 yuan per tonne, their highest in 2-1/2 years.
While the market is entering 2017 on its most robust footing in years, worries about China's economic growth linger.
"The Chinese economy is likely to stagnate in 2017, so the macro-economic background might go against the steel market," said Zhou Guangyan, steel analyst at Zhongcai Futures.
Beijing is expected to ramp up its efforts to make its bloated steel sector more efficient, by getting rid of excess capacity and cutting emissions.
This year, it slashed 45 million tonnes of capacity, but most of that permanently shuttered plants that were already idled. In 2017, cuts may have a more material impact on supplies of critical raw materials like scrap and iron ore.
This year has been stellar across the steel markets.
Iron ore prices have had their best year since 2013 after mills have chased top-quality raw material to meet tougher environmental standards even as domestic inventories have hit their highest in almost 2-1/2 years this month. CUS-STKTOT-IORE.
The most-active coking coal futures on the Dalian Commodity Exchange settled up 1.63 percent at 1,182 yuan per tonne, after falling to the lowest since Oct. 18 on Tuesday.
Coke has more than quadrupled this year to around 1,500 yuan per tonne, while coking coal has more than doubled to just under 1,200 yuan per tonne. ($1 = 6.9468 Chinese yuan) (Editing by Christian Schmollinger and Subhranshu Sahu)