BEIJING :China's Sinopec has signed an equity agreement with Kazakh state-owned oil and gas firm KazMunayGas JSC (KMG) for a 30 per cent stake in a planned polyethylene project in Kazakhstan, Sinopec said in a statement on Tuesday.

The companies previously said they had agreed "key terms" for the project in May this year, on the sidelines of the China-Central Asia summit.

The project, located in western Kazakhstan's Atryau region, has a design annual capacity of 1.25 million tons per year, the statement said.

The total cost of the project is $7.7 billion, Kazakh state news agency Kazinform reported on Tuesday.

The announcement comes during a visit by Kazakh President Kassym-Jomart Tokayev to Beijing for the Belt and Road Forum, where Tokayev and China's President Xi met and discussed increasing cooperation in investment and trade.

Sinopec chairman Ma Yongsheng said the company planned to begin construction of the plant in the second half of 2024, Kazinform reported.

Sinopec and KMG also signed a pre-feasibility joint development agreement to study the possibility of investing in the construction of PTA (phthalic acid) and PET (polyethylene terephthalate) plants in Kazakhstan, the Sinopec statement added.

China's three main state-owned oil firms Sinopec, PetroChina and CNOOC have all previously made investments in Kazakhstan's oil and gas sector. PetroChina is a member of the consortium that is currently developing the Kashagan field in the Caspian Sea - Kazakhstan's second-largest producing field - alongside Western oil majors and KMG.

On Monday, CNOOC signed a memorandum of understanding with KMG, which included an agreement to conduct joint geological research as well as expand cooperation on existing oilfields, according to Chinese state media.