A major US-Mexico border crossing in San Diego was closed for hours after a group of migrants on the Mexican side rushed the border area, leading American Border Patrol agents to fire tear gas at the group.
About 500 migrants on the Mexican side of the border overwhelmed police blockades near the San Ysidro Port of Entry on Sunday afternoon, authorities in Tijuana told CNN.
As the migrants tried to cross the border, authorities on the US side used tear gas to disperse them.
Video of the scene showed a cloud of tear gas that sent people running and screaming, including families with young children.
US Customs and Border Protection said the migrants threw projectiles that struck several agents.
"Border Patrol agents deployed tear gas to dispel the group because of the risk to agents' safety," the agency tweeted.
The San Ysidro Port of Entry, which closed to vehicle and pedestrian traffic for several hours, was reopened later on Sunday.
Mexico's Interior Ministry said federal and local authorities stopped the migrants from crossing the border illegally.
Those identified as having tried to illegally cross will be processed for deportation to their home countries, it added.
By Sunday night, Tijuana police had arrested 39 people, the agency said on Facebook.
The Interior Ministry described Sunday's incident as "acts of provocation" and warned that far from helping the migrants' cause, it could result in a serious incident on the border.
In response to the incident, US Secretary of Homeland Security Kirstjen Nielsen said: "The DHS will not tolerate this type of lawlessness and will not hesitate to shut down ports of entry for security and public safety reasons.
"We will also seek to prosecute to the fullest extent of the law anyone who destroys federal property, endangers our front-line operators, or violates our nation's sovereignty."