Southwest Airlines and WestJet, the biggest US and Canadian low-cost carriers, have agreed to an operating and marketing partnership that will extend their reach into neighbouring international markets.

The co-operation, which is expected to include co-ordinated and shared flight schedules, reciprocal frequent-flyer programmes and joint ground-handling operations, marks Southwest’s first alliance with a foreign carrier, while broadening WestJet’s horizons in its rivalry against Air Canada.