(Reuters) -Archer Aviation ( ACHR ) on Monday said it signed a partnership with Korean Air to commercialize its electric air taxis in South Korea, with a potential purchase of up to 100 aircraft.

The deal underscores an intensifying race among electric vertical take-off and landing developers to win regulatory approvals, lock in airline partners and move from prototypes to paid service.

Shares of the Santa Clara, California-based company rose 6% in early U.S. trading.

Startups and aerospace incumbents alike are pitching short urban hops and airport transfers as faster, lower-emission alternatives to congested ground transport, even as the sector contends with certification hurdles, infrastructure build-out and uncertain timelines to profitability.

Archer said the agreement targets deployment of its Midnight eVTOL "across multiple applications and use cases, starting with government applications."

The aircraft is designed for 10-20 minute flights and last month completed a series of performance test flights, with two of its highest-altitude flights to date.

Backed by Boeing and Stellantis, Archer is producing six aircraft at two U.S. plants and counts United Airlines and the owner of India's IndiGo among its customers.

Archer, which is yet to turn a profit, expects an adjusted EBITDA loss of $110 million to $130 million in the third quarter, wider than last year's $93 million loss.

Last week, Archer said it won a bid to acquire rival Lilium's portfolio of about 300 advanced air mobility patent assets for 18 million euros ($21 million), expanding its own portfolio to over 1,000 patent assets.

($1 = 0.8575 euros)