TIJUANA, Mexico (AP) — Protesters took control of vehicle lanes at one of the busiest crossings on the US border Sunday to oppose Mexican gasoline price hikes, waving through motorists into Mexico after Mexican authorities abandoned their posts.

Motorists headed to Mexico zipped by about 50 demonstrators at the Otay Mesa port of entry connecting San Diego and Tijuana, many of them honking to show support. The demonstrators waved signs to protest gas hikes and air other grievances against the government of Mexican President Enrique Pena Nieto.

Other protests closed southbound traffic for hours at the San Diego-Tijuana San Ysidro port of entry, the busiest crossing along the 2,000-mile border, and halted southbound traffic at one of two crossings in Nogales, Arizona.

US Customs and Border Protection and California Highway Patrol officers closed southbound Interstate 5 to block access to the San Ysidro crossing, diverting traffic several miles east to the Otay Mesa port of entry.

Inspections were normal for all travellers entering the US from Mexico. A CBP statement said that Mexico-bound motorists were directed to the other crossing for 5 1/2 hours at the request of Mexican authorities.

The demonstrations, which are unrelated to the election of US President Donald Trump, have disrupted Mexican border crossings for weeks. Earlier this month, police in the Mexican state of Sonora fought a pitched three-hour battle to free a border rail crossing at Nogales that had been blocked by people protesting the 20 per cent nationwide hike in gasoline prices that took effect on New Year’s Day.

Only a small percentage of motorists entering Mexico from the US are stopped for inspection under normal circumstances, but Sunday’s demonstration gave them an open invitation. Guns and cash from drug sales in the US are often introduced to Mexico by car.

Protesters said Mexican customs officials retreated within minutes after they arrived at the Otay Mesa crossing. About two hours later, a Mexican soldier stood by, but there were few other signs of government presence.

“We’re exercising our right to free speech,” said Brenda Cortez, a 22-year-old college student from Tijuana. “It’s to make sure we are noticed.”