China ride-hailing giant Didi Chuxing — the world’s biggest rival to US-based Uber — has raised over $4bn in its latest round of funding, valuing the company at over $50bn and setting it on course of international expansion.

The latest major funding round is Didi Chuxing’s second this year. It announced a $5.5bn round in April, the largest-ever round for a tech company.

It’s thought Didi Chuxing’s latest valuation is higher than Uber can expect from its ongoing round — potentially making Didi the world’s most valuable startup for the first time and knocking Uber from the top spot.

Now Didi Chuxing wants to mount an international challenge to Uber after already winning a local war when it acquired Uber’s China business in 2016.

Earlier this month, Didi Chuxing was linked with an expansion to Mexico, according to Reuters, while Bloomberg reported that it is eyeing a move into Taiwan using a franchise model.

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So far Didi has grown internationally only though investment in Uber’s rivals. It’s put money into Lyft in the US, Taxify in South America and Europe, Careem in the Middle East, Ola in India, and Grab in Southeast Asia.

The company has said it also plans to spend the extra cash from this funding round on a fleet of 1m cleaner energy cars and a network of charging stations.

Didi already claims to operate the world’s largest fleet of electric cars with 260,000 of the 2m electric vehicles currently on the road in China using its platform.

The company’s goal is to increase that amount to 1m electric vehicles by 2020.

Didi has has also been investing in artificial intelligence and self driving cars for its ride-hailing service, opening an AI research lab in the US earlier this year.

Japanese telecom group Softbank — which has invested far and wide in recent years — and United Arab Emirates investment vehicle Mubadala have joined iPhone maker Apple and Chinese e-commerce giant Alibaba in putting cash into Didi.

In total, Didi claims some 450m users around the world and 21m drivers across its ride-hailing app and taxi, minibus, and car rental services.