A molasses spill in a river in El Salvador from a sugarcane processing plant has triggered an alert by authorities worried about the effect on fish and people along the waterway.

The civil protection service issued the alert after 3.4 million liters (900,000 gallons) of sludgy, brown, hot molasses was released into La Magdalena river near the town of Chalchuapa, 55 kilometers (35 miles) west of the capital San Salvador.

More than 450 families on or near the river depend on its waters for their daily household and farming needs. 

The environment ministry said the spill occurred on Thursday.

The civil protection service said efforts were being made to try to collect the molasses.

Photos on local media websites showed workers shoveling up some of the viscous brown mess along the river bank.