The Hungarian tax authority has fined Uber drivers in its first probe against the ride-sharing service which the economy ministry says "ignores passenger safety" and must be made to follow regulations.

The taxmen used Uber services randomly and said they found several irregularities: drivers did not have tax numbers, nor did they give receipts after the ride, and they did not possess taxi licences.

The economy ministry statement said drivers could face up to 200.000 forints in fines, but did not specify how many drivers were checked or fined.

The authorities on Saturday vowed "to make the company operating Uber network - which drains the budget and ignores passenger safety - adhere to the rules," the ministry statement said, adding that the probe will continue.

The popular but controversial taxi app for mobile phones puts customers in touch with private drivers at prices lower than those of traditional taxis, but it is facing legal challenges and limits on its activities in the European Union.

Uber said efforts by national governments to shut it down breached EU laws on competition and the single market.

Taxi firms say Uber should be regulated the same way as taxi services.