MEXICO CITY, (Reuters) – Hundreds more people have joined a caravan of thousands of migrants in Mexico bound for the United States, one of the organizers said, as the group traveled through the southern state of Chiapas.

Organizer Irineo Mujica said the caravan had swelled since Monday by about 1,000 to more than 7,000 people, although a spokesperson for the Chiapas government said state authorities still estimated its size at around 3,500 participants.

On Tuesday the caravan was resting in the municipality of Huehuetan, about 16 miles (25 km) from Tapachula, a city near the Guatemalan border from which the migrants set off.

On Wednesday, the caravan will aim to reach the town of Huixtla, about 13 miles to the north, Mujica said.

U.S. President Joe Biden, who is seeking reelection next year, is under pressure to bring down the number of people crossing illegally into the United States from Mexico.

Most of the latest caravan are from Cuba, El Salvador, Guatemala, Haiti, Honduras and Venezuela, according to Mujica.

Many migrants are fleeing poverty and political instability in their homelands, and this year has seen record numbers crossing the Darien Gap region connecting Panama and Colombia.

Tropical storm Pilar dumped heavy rains on the western coast of El Salvador on Tuesday, leaving two people dead. The storm is also threatens to lash southern Mexico with rain, potentially affecting the region where the caravan is traveling.