The Pentagon shrunk the size of its delegation traveling to the Singapore Airshow and US defense firms Lockheed Martin Corp and Raytheon Co said they would not attend, as the impact of the coronavirus has reduced participation in the event.

Undersecretary of Defense Ellen Lord will no longer attend the event "due to extenuating circumstances", Lieutenant Colonel Mike Andrews said in a statement. Lord is the Pentagon's chief weapons buyer and was the Pentagon's lead representative at the event. Other Pentagon leaders including uniformed military officials plan to attend.

Lockheed Martin became the first major US defense company to announce it will not attend the airshow due to the coronavirus. "We determined this was in the best interest of our employees and aligned with the US Department of Defense's decision to reduce its presence," Lockheed said in a statement.

Raytheon also pulled out. "Because of the growing health crisis in the region, and out of an abundance of caution, Raytheon Company will not be exhibiting at this year's Singapore Airshow," it said in a statement.

The airshow will continue next week, but organizers might look to limit public visitors, a Singaporean official said on Friday, as Singapore reported three more coronavirus cases that authorities have not yet linked to previous infections or travel to China.

The new cases take Singapore's virus tally to 33 with the alert level raised to orange, denoting the disease is severe and passes easily from person-to-person. Red - the highest alert level - indicates it is spreading widely.

The trade portion of the airshow, held every two years, is due to begin on Feb. 11. Business jet manufacturers Bombardier Inc,, Textron Inc and General Dynamics Corp's Gulfstream division are also among those to have pulled out of the airshow.