More than a dozen ambulances were seen rushing to Riyadh’s ‌international airport and travellers were evacuated from parts of the facility after a loud blast was heard there on Saturday, an eyewitness and people briefed ​on the matter said.

Saturday’s incident comes amid an escalation of missile ​strikes by Yemen’s Iran-aligned Houthi on the kingdom. The airport has already been attacked twice this week, leaving four people ​dead and others wounded, and badly damaging an aircraft.

The Saudi government’s media ​office and the Saudi civil aviation authority did not immediately respond to requests for comment on the incident.

Flight tracking site flightradar24 showed all flights to Riyadh ​had either been diverted or cancelled, with only a helicopter ​hovering over the airport at one point.

The airport urged passengers to contact their airlines ‌directly and check their flight status before heading there.

Etihad Airways and Qatar Airways cancelled multiple flights between their respective hubs and Riyadh, with some cancellations extending into Monday.

Houthi attacks on Thursday and earlier in ​the week had ​already prompted a number of carriers to suspend or cancel services to the Saudi capital, shortly before Riyadh is due ​to host major energy and investment conferences.

Organisers of those ​conferences said on Saturday they would go ahead as planned, and they sought to reassure attendees of their security.

The Houthis have said airliners should avoid Saudi ​airspace, declaring it a zone of military ​operations after the Saudi-backed Yemeni government launched an offensive against the group earlier this ​month.