* Xuzhou steel mills face tougher emissions standards

* At least 3 mills shut in crackdown -sources

* Those mills account for third of city’s steel capacity (Adds comment, detail)

By Muyu Xu and Josephine Mason

BEIJING, April 27 (Reuters) - At least three steel mills in the Chinese city of Xuzhou, in the nation’s No. 2 steelmaking province, have suspended operations amid local authority orders to shut plants until they meet tough anti-pollution rules, three industry sources said.

Those three plants have combined a capacity to produce 4.25 million tonnes of steel a year, a third of the capacity in the city in the eastern province of Jiangsu. The status of other mills in Xuzhou remains unclear.

China, the world’s top steel producer, has ordered a host of cities to crack down on heavy industry as part of its years-long war on smog, which has become a hot-button social issue amid concerns about damage to people’s health.

A sales manager at Liguo Zhenbei Steel Co, which operates one of the closed mills, said local authorities had ordered all steel plants in the city to shut until they meet the latest tough requirements aimed at cleaning its notoriously toxic air.

“Mills, no matter big or small, have all stopped operations,” he said, declining to give his name as he is not authorised to talk to media.

The city’s environmental bureau declined to comment.

Xuzhou Dongnan Steel Industrial Co Ltd, one of the city’s biggest steel mills by production capacity, is temporarily closed for maintenance, an official told Reuters by phone. The official did not say how long the plant would be shut.

Earlier this month, the city launched six months of environmental inspections at industrial plants and construction sites as part of its 2018 action plan to clean its skies.

“At the beginning, I thought my mill would be exempt from the closure list, since our mill emits less harmful substances,” said a deputy general manager at an electric-arc furnace (EAF) in the city.

He said his family name was Wang, but declined to give his first name. He did not want the company he works for to be identified.

EAFs, or mini-mills, use scrap steel and emit far less carbon than blast furnaces, which have to go through the polluting sintering process to make hot metal.

However, Wang’s mill last week was also ordered to close until it can pass a test conducted by a third-party environmental detection agency. That is unlikely to happen before the end of May, he said.

Xuzhou is a hub of 13 million tonnes of steelmaking capacity in the eastern province of Jiangsu, China’s second-biggest steel producing province after Hebei.

The city is under particular pressure to deal with the problem because its average concentration of hazardous, breathable particles known as PM2.5 rose by 10 percent in 2017, missing the national target for a 20-percent cut.

Average PM2.5 levels for April so far have been 110 micrograms per cubic metre, up from the same time last year and almost double the city’s 2018 aim to drop to below 60 micrograms, according to data from China’s National Environmental Monitoring Centre. (Reporting by Muyu Xu, Josephine Mason and Beijing newsroom; Editing by Richard Pullin and Joseph Radford)