The US state department for travel said the gunfire was coming from the rear of the building. It urged any travellers to seek shelter in place. The first report of gunfire was issued at around 12.50pm local time.
The travel alert said the staff had taken shelter inside the embassy. "If you are traveling to the embassy, find a safe area to shelter," it wrote on Twitter.
State Department officials did not immediately have further details on the incident, including whether it was ongoing.
Haiti, one of the world's poorest countries, witnessed widespread riots in February when thousands of people took to the streets demanding better living conditions. Haiti's President Jovenel Moise earlier this month appointed a new prime minister to tackle mounting problems, including insecurity in the capital.
Haiti won independence from France in 1804, making it the second-oldest republic in the Western Hemisphere.