HOUSTON, Feb. 28 (Xinhua) -- Navajo Technical University in northwest New Mexico was at Code Green and resumed normal classroom instruction and work Wednesday afternoon after a potential threat alert has been lifted.

Earlier Wednesday morning, the university, about 300 km west of Santa Fe, the capital city of New Mexico, the United States, was on lockdown following Code Red alert. The university degraded the alert to Code Yellow several hours later.

According to the post on the website of the university, the Code Yellow alert means there is a threat or a potential threat outside of the campus.

The procedures for the Code Yellow alert includes: locking all exterior doors, setting security checkpoint at all main entrances and screening all visitors.

Meanwhile, a precautionary lockdown placed on Santa Fe High School was lifted Wednesday afternoon.

The Santa Fe High School was placed on lockdown around noon time Wednesday as a precautionary measure as a result of a report of popping sounds thought to be gun shots heard outside the school and in the area.

The police and Santa Fe law enforcement officials responded to ensure that students were safe and no threat was present.