SINGAPORE, Oct 31 (Reuters) - At least three Chinese companies including state giant China National Offshore Oil Company (CNOOC) are evaluating Shell's Singapore assets and considering non-binding bids in coming weeks for the city-state's oldest refinery, according to several sources familiar with the matter.

Reuters reported in August that Shell had hired Goldman Sachs to explore a potential sale of its refining and petrochemical plants in Singapore as part of a broader strategic review globally to become a lower-carbon operator.

A buyer of Shell's assets on Bukom and Jurong islands would gain a foothold in Asia's main oil trading hub but would also face competition from newer refineries elsewhere - the Bukom facility opened in 1961 - as well as a Singapore carbon tax set to rise sharply in 2024.

CNOOC, Eversun Holdings and Wanhua Chemical are among those that have started early evaluations of Shell assets that include a 237,000 barrels per day (bpd) refinery and a one million metric ton per year (tpy) ethylene cracker, the sources said.

CNOOC, the parent of offshore oil and gas major CNOOC Ltd , operates a joint refining-petrochemical complex with Shell in southern China.

CNOOC did not immediately respond to a request for comment.

The companies are among more than a dozen Shell invited to explore interest in the facilities. They also included Chinese state majors Sinopec, PetroChina as well as big independent refiners Rongsheng Petrochemical and Hengli Petrochemical, two of the sources said.

However, Sinopec Corp's president said in late August it was not interested in the Shell assets. Senior company officials at Hengli Petrochemical and Rongsheng told Reuters that the companies had no plan to bid for the assets.

PetroChina and its parent China National Petroleum Corp (CNPC) did not immediately respond to requests for comment.

"It appears that Shell has invited a broad group of companies and asked interested parties to send in a non-binding bid and proposal as to how they plan to run and manage the facilities," said a person involved in assessing the assets.

Two of the sources said Shell had set a preliminary Nov. 5 deadline for proposals, although that could be extended.

In response to questions from Reuters, Shell said the strategic review of its energy and chemicals park assets in Singapore is ongoing and it is exploring several options including divestment. It declined to comment on bidders or a schedule.

Goldman Sachs declined to comment.

It could not be determined which other companies may be assessing the assets.

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CNOOC's joint venture with Shell in Huizhou, Guangdong province, produces plastic raw materials ethylene, propylene and derivatives. The companies agreed in 2020 to expand the complex in the next three years.

Privately-run Eversun Holdings, based in Fujian province, started as a nylon producer and is building a 900,000-tpy polypropylene plant in Putian, according to its website.

Eversun did not respond to a request for comment.

Shandong province-based Wanhua Chemical is the world's largest feedstock supplier for polyurethane foam used in home furnishings and building insulation, and is a leading player in chemicals used in solar panels and lithium batteries.

A Wanhua spokesperson said he was not aware of the company's potential interest in the Shell assets.

For Chinese would-be bidders, Singapore could be a base to produce and secure feedstocks to produce petrochemicals in China as well as a launchpad to expand global trading and marketing, especially in fast-growing Southeast Asia, experts said.

"The key draw for Chinese companies is to have some form of upstream feedstock integration in Southeast Asia should they decide to expand on downstream petrochemical derivative production and activity within the Southeast Asia region," said Wood Mackenzie's global head of polyesters, Salmon Lee. (Reporting by Chen Aizhu and Trixie Yap; Editing by Tony Munroe, Florence Tan and Kim Coghill)