The San Ysidro port of entry is temporarily closed after a construction structure collapsed around 11 a.m. Wednesday, falling on at least one vehicle, according to several eyewitnesses.

They said that all traffic was being rerouted back to Tijuana through one gate at the extreme left-hand side of the port of entry, causing chaos for the thousands of motorists waiting to cross.

"The U.S. Customs agents told us that we had to go back, that we had to go through Otay," said Iñaki Zárate, a Chula Vista resident who said he was about ten cars away from entering the United States when the accident happened.

U.S. border authorities did not initially return phone calls. There was no initial information about possible injuries.

An estimated 50,000 cars cross daily at the San Ysidro port of entry, which is undergoing a major expansion project.