About 400 Central American migrants have crossed into Mexico with the aim of reaching the U.S. border to request asylum.

Mexican police looked on as about half the migrants crossed the Suchiate River on inner-tube rafts Tuesday. The mainly Honduran migrants then walked into the border city of Ciudad Hidalgo to rest in the main plaza.

The other half of the migrants walked over the bridge that connects Mexico and Guatemala and waited to register at a Mexican immigration office. They included many women and children.

Mexico has been discouraging mass marches down highways, as migrant caravans did in past months.

The border crossing comes after U.S. President Donald Trump threatened to slap tariffs on Mexican imports unless Mexico does more to stop the passage of migrants through its territory.