SINGAPORE - China has given five state-owned companies until Thursday to report on their use of imported oil over the past years, part of a broader effort to regulate crude imports into the world's largest oil importer.

In an "urgent notice" dated May 25 and reviewed by Reuters, the National Development and Reform Commission (NDRC) requested that Sinopec Group, China National Offshore Oil Corp (CNOOC), Sinochem Group, ChemChina, and China North Industries Group provide historical information on their crude usage.

Specifically, the companies must give information on whether they have engaged in the reselling of their crude imports to other companies and to investigate the usage of their crude at refineries that operate under a so-called tolling scheme that reduces the companies' tax payments.

The NDRC did not immediately respond to a request for comment.

It was not immediately clear why the government is examining the imports of these state-run companies since they are not subject to crude oil import quotas even though they regularly supply crude to independent refiners that are subject to the quotas.

The information request is part of a broader overhaul the Chinese government has embarked since early this year to tackle a worsening domestic fuel surplus and lost tax revenues due in part to unchecked flows of imported crude oil to refiners that are not part of the import quota system, said two senior oil trading officials in Beijing.

The investigation also follows a separate inspection in April by the NDRC of independent refiners in the eastern province of Shandong into plants the companies pledged to close in return for winning import quotas, Shandong-based industry sources said.

That inspection also covered usage of crude oil import quotas, as several independent plants in Shandong were found trading off quotas to refiners not qualified for processing imported crude oil, said the sources.

(Reporting by Shu Zhang, Florence Tan and Chen Aizhu; Editing by Clarence Fernandez and Christian Schmollinger) ((shu.zhang@thomsonreuters.com; +65-6870-3549; Reuters Messaging: Twitter @shuzhang4))