Party leaders worry about the dominance of China's biggest internet companies including Alibaba at a time when the industry is expanding into finance, health services and other sensitive areas. The party says anti-monopoly enforcement, especially in tech industries, is a priority this year.

Alibaba was fined for "abusing its dominant position" to limit competition by retailers that use its platforms and hindering the "free circulation" of goods, the State Administration for Market Regulation announced. It said the fine was equal to 4 per cent of its total 2019 sales.

The move is a new setback for Alibaba and its billionaire founder, Jack Ma, following a decision in November by regulators to suspend the stock market debut of Ant Group, a finance platform spun off from the e-commerce giant. It would have been the world's biggest initial public stock offering last year.

Ma, one of China's richest and most prominent entrepreneurs, disappeared temporarily from public view after criticising regulators in a November speech. That was followed days later by the Ant Group suspension, though finance specialists said regulators already had been worried Ant lacked adequate financial risk controls.

Alibaba, launched in 1999, operates retail, business-to-business and consumer-to-consumer platforms. It has expanded at a breakneck pace into financial services, film production and other fields.

In February, the government issued anti-monopoly guidelines aimed at preventing anti-competitive practices such as signing exclusive agreements with merchants and use of subsidies to squeeze out competitors.

Regulators said in December they were looking into possibly anti-competitive tactics by Alibaba including a policy dubbed "choose one of two,'' which requires business partners to avoid dealing with its competitors.