Dalian and Singapore iron ore futures dropped below $100/t on Tuesday, while spot prices slumped to the lowest in a week, pressured by renewed worries over Covid-19 curbs and steel output restrictions in top producer China.

The most-traded January iron ore contract on China's Dalian Commodity Exchange fell as much as 4.1% to 688.50 yuan ($99.51) a tonne, the weakest since Aug. 23.

On the Singapore Exchange, the steelmaking ingredient's most-active October contract was down 3.4% at $98.40 a tonne, as of 0347 GMT.

Steel prices also stretched losses after authorities in China's southern city of Shenzhen shut the world's largest electronics market of Huaqiangbei and suspended service at 24 subway stations on Monday in a bid to curb a Covid-19 outbreak. Read full story

Rebar on the Shanghai Futures Exchange fell 3.1% while hot-rolled coil dropped 2.4%. Stainless steel lost 1.2%.

The epidemic remains a "severe challenge" for China's vast ferrous commodities industry as lockdowns are reducing demand for steel products and inputs, Huatai Futures analysts said in a note.

China's strict zero-Covid policy and a property sector downturn have caused its economy to slow down sharply this year.

Steel production control to curb emissions in the world's biggest iron ore consumer is also denting demand for other steelmaking ingredients.

In Tangshan, China's biggest steel-producing city, authorities and mills reportedly met on Friday to discuss capacity reduction targets.

To meet its target, Tangshan's average daily output for the rest of the year should be less than 314 700 t, compared with 352 300 t over January to July, based on a calculation by industry information provider Mysteel.

Dalian coking coal tumbled 5.5% and coke slumped 4.4%.

In the spot market, benchmark 62%-grade iron ore bound for China traded at $104.50/t on Monday, the lowest since August 22, based on SteelHome consultancy data.