Molasses gushed into a river in El Salvador when a sugar refinery vat sprang a leak Thursday, a month after a similar spill triggered a state of environmental emergency.

"It's a large-scale spill. It's going straight into the Las Canas river," Environment Minister Lina Pohl told Radio Nacional.

Officials were still estimating how much of the sludgy brown substance seeped into the river.

The spill occurred near the town of Apopa, just north of the capital San Salvador, when a giant vat used to store millions of gallons of molasses ruptured, the El Salvador Sugar Association said in a statement.

Technicians are working with a 60-person team and heavy equipment to "mitigate the impact," association spokeswoman Melissa Mendez told AFP.

No victims were immediately reported.

The environment minister said workers were building natural barriers to contain the viscous brown mass.

Another spill on May 5 dumped 3.4 million liters (900,000 gallons) of molasses into La Magdalena river, just west of San Salvador, eventually spreading to two other rivers.

That spill caused a mass die-off of fish and raised fears for local residents, prompting authorities to declare a three-month state of emergency in the affected area.