German telecom operator Deutsche Telekom has reported record profits for 2019, with US unit T-Mobile gleaning millions more customers ahead of a merger with competitor Sprint.

The bottom line bounded almost 80% year-on-year to €3.9 billion, making 2019 "the most successful year in the history of the company", Deutsche Telekom said in a statement.

The operator was now the "clear number one in our industry in Europe", it added.

For 2020, Deutsche Telekom said profit from operations was likely to be stable, and sales on the rise, even without counting in the effects of the Sprint-T-Mobile tie-up.

Years of rapid growth in its American subscriber base meant T-Mobile already accounted for around half of the group's €80 billion in annual turnover in 2019, compared with just over a quarter for home market Germany.

With the Sprint takeover, recently given the go-ahead by a federal court, the company's US subscriber numbers will leap to over 100 million.

Bosses say that will give T-Mobile the scale to compete with the sector's giants Verizon and AT&T.