Chile's development agency Corfo said any purchase of a stake in SQM by Tianqi Lithium or associated entities would "gravely distort market competition", given Tianqi and SQM together controlled 70% of the global lithium market, according to a 45-page complaint filed on Friday, the wire service said.

Corfo head Eduardo Bitran told Reuters Tianqi had presented a non-binding offer for Nutrien Ltd's 32% stake in SQM, which regulators had ruled Nutrien must divest as part of its creation from the recent Saskatchewan Potash/Agrium merger.

Bitran - who was expected to leave his post on the weekend when Sebastian Pinera was sworn in as Chile's new president - said an SQM stake would give China an unfair advantage in the global race to secure resources for the EV market, Reuters reported.

"Yes, we are very worried on the distortions that the sale of Agrium stake on SQM could create in the global lithium market and electro mobility," Bitran tweeted on Sunday.

Chilean antitrust regulator FNE would need to review the complaint, Reuters said.

Corfo and SQM reached agreement in January allowing SQM to up its lithium production quota, a move that rocked global lithium stocks.