LISBON, Portugal (AP) — Lisbon's growing popularity with foreigners is compelling the Portuguese government to adapt a military airport for commercial flights.

The government says it plans to modify the little-used Montijo air base on the south side of the River Tagus because the capital's sole international airport is nearing its capacity of 22 million passengers a year.

The number of visitors to Lisbon grew by more than 8 percent last year, after a 5 percent increase in 2015.

Officials said Wednesday they hope the new airport will be operational by 2022. The modification work, which requires approval from environmental authorities, is expected to cost up to 400 million euros ($422 million).

Passengers arriving in Montijo will travel 13 kilometers (8 miles) by ferry or 32 kilometers (20 miles) by road into Lisbon.