Central American migrants and volunteers were reportedly attacked outside the makeshift Benito Juarez shelter in Tijuana, near the US-Mexico border, on Wednesday.
Honduran Maria Isabel Lopez said that the attackers threw water and spat on migrants. Containers of urine were also apparently thrown.
Those who came to help added that police stopped them from accessing the area.
"Right now, we came to leave them [clothes], but they forbade us from entering. The rains are coming and we brought tents for the people, but [the police] do not want to [allow us to help]. They don't want to," said volunteer Adriana Cervantes.
Last week the city authorities started to relocate migrants from the shelter at the Benito Juarez Sports Centre to a new facility El Barretal due to unsanitary conditions.
Some migrants refused to leave, citing increased distance from the border.
While promising not to carry out any forced evictions, officials cut off services at the Benito Juarez Sports Centre in order to force migrants to leave the area.
Over 5,000 migrants from Central America have been waiting near the US border after travelling over 4,000 km (2,500 miles) in the migrant caravan. They say they are seeking asylum in the US to escape poverty and violence in their home countries.