German premium carmakers took a further hit to their Chinese sales in the first quarter, data from the companies showed on Wednesday, with Porsche and Mercedes-Benz also struggling with supply chain troubles.

Sales in China fell 3.8% at BMW, 12% at Mercedes-Benz and 24% at Porsche, the companies said, indicating that efforts by authorities and automakers to jumpstart demand in the world's second-biggest economy are not yet seeing results.

Porsche's sales in North America, down 23%, were disrupted after 1,000 Porsche cars and SUVs, as well as several hundred Bentleys and several thousand Audi vehicles, were impounded by customs officials at U.S. ports because a Chinese subcomponent breached anti-forced labour laws.

Mercedes-Benz said it also suffered from supply chain bottlenecks in Asia, but did not provide details.

Both carmakers said model changes hampered sales in the first quarter, with Mercedes-Benz ramping up the E-Class in China and Porsche updating its Panamera and Taycan models.

Carmakers are facing a challenging year, forecasting stable or lower returns and slower sales growth as they invest in revamping their line-ups to tackle growing competition against a backdrop of muted demand, especially for all-electric cars.

All three carmakers are launching a swathe of new all-electric models and updating combustion engine offerings as they battle to revive auto sales still below pre-pandemic levels and tackle competition from China and elsewhere.

German autos association VDA reported earlier this month that total sales in the first quarter were above last year's figures but remained 21% below 2019 sales. (Reporting by Victoria Waldersee Editing by Mark Potter)