There was a shooting involving officers at the border crossing near San Diego on Monday night, after a pickup entering the United States failed to stop for an inspection, Customs and Border Protection said in a statement.

There were no injuries to Customs and Border Protection officers, a union leader told the local newspaper. The CBP statement did not say whether officers were fired upon, or if anyone was hit or arrested.

The incident occurred around 7:30 p.m.at the San Ysidro port of entry, which separates the San Diego area and Tijuana. "The driver failed to stop for an inspection, and there was an officer-involved shooting," a CBP spokesperson said in a statement.

No further details were released, and CBP referred questions to the San Diego Police Department, which the spokesperson said was the lead investigative agency in the incident.

A San Diego police watch commander said there was a shooting but did not know if anyone died or was wounded. He said that police homicide detectives were conducting an investigation and would release more information later.

A leader from the San Diego branch of the National Treasury Employees Union, which represents Customs and Border Protection officers, said in a text message to The San Diego Union-Tribune newspaper that "all officers involved are safe and uninjured."

Video captured by bystanders includes what appears to be sounds of a burst of gunfire. Another video shows officials taking cover. Video obtained by NBC San Diego shows what appears to be a warning for people to get down amid the gunfire.

A driver waiting to cross the San Ysidro Port of Entry was recording when dozens of shots rang out during an incident involving Border Patrol agents. We'll have the latest info coming up on the NBC 7 News at 11 p.m. https://t.co/iXEwQpN7XD pic.twitter.com/zhxFf9z20o — #NBC7 San Diego (@nbcsandiego) June 4, 2019

"We hear 'pop pop pop pop pop pop.' Super gnarly. We're like, no way, those were fireworks," Zooch Williams, who was on the Mexican side of the border waiting in line to cross, told NBC San Diego. "Our other buddy is like, 'no way, those were gunshots.' I'm like, 'bro, I hunted as a kid, not gunshots.' And then we see all these Border Patrol dudes running, and they started running down and chasing someone."

The San Ysidro port of entry, separating southern California and Tijuana, has been called one of the busiest land border crossings in the world.

The federal General Services Administration says in its website that the San Ysidro Land Port of Entry is the busiest in the Western Hemisphere, with around 70,000 northbound vehicles processed each day.

"U.S. Customs and Border Protection is cooperating with investigations by other law enforcement agencies," the CBP spokesperson said in a statement. "Per CBP policy, the agency will also conduct an internal review of the incident."