BERLIN, May 6 (Reuters) - BMW's BMWG.DE pre-tax earnings slumped by 25% in the first quarter of the year and its core operating margin narrowed, but the German premium carmaker still beat estimates as it faces tariff costs and a difficult market in China.

BMW said on Wednesday its pre-tax earnings came in at 2.3 billion euros ($2.70 billion) in the first quarter, compared with analysts' forecast of 2.2 billion euros in a company-provided consensus. Group revenue fell by 8.1% to 31.0 billion euros.

The EBIT margin in the carmaker's core automotive business stood at 5.0% in the first three months of the year, beating analysts' forecast of 4.7%.

($1 = 0.8522 euros)