They say that joining a large group offers more protection against police officers and bandits.
A larger group of at least 3,500 Hondurans, left that country in mid-October and is now in southern Mexico making its way to the US.
Press TV reports: Dozens of the Salvadorans had arrived at the Guatemalan border by Sunday afternoon and were having their documents checked.
The Hondurans, which had left their country in mid-October, are now in southern Mexico, which is hosting some 7,000 to 14,000 US-bound Central American migrants, mostly Hondurans, according to UN figures.
A third caravan of Central American migrants has also been moving through Guatemala.
Also on Sunday, hundreds of migrants in that group — which originally numbered over 1,000 before splitting — broke through a gate at the Guatemala border with Mexico in Tecun Uman on Sunday, prompting clashes with police.
Local sources said security forces used rubber bullets against the asylum seekers, and that one person, Honduran Henry Adalid, 26, was killed.
Central American migrants say they are escaping from violence, corruption and unemployment at home. They believe travelling in caravans would better ensure their safety while passing through violence-hit Mexico before reaching the US soil.
The US-bound migrants are defying threats from President Donald Trump to deploy troops to the border to prevent their entrance.
Trump and his fellow Republicans have sought to highlight the immigration “crisis” ahead of the midterm elections scheduled for November 6, in which the party is battling to keep control of Congress.
Homeland Security Secretary Kirstjen Nielsen on “Fox News Sunday” said Trump was determined to exercise all his power to stop asylum seekers from crossing the border into the US.
“We have a crisis at the border right now … This caravan is one iteration of that but frankly we essentially see caravans every day with these numbers,” she said of the 3,500-strong group of Hondurans in southern Mexico.
“I think what the president is making clear is every possible action, authority, executive program, is on the table to consider, to ensure that it is clear that there is a right and legal way to come to this country and no other ways will be tolerated,” Nielsen added.
Trump has made his hard-line stance on immigration an integral part of his presidency and has promised to build a wall along the US-Mexican border to curb the flow of migrants from Mexico and Central America into America.