LONG BEACH, Calif. — At least 1.5 million gallons of sewage spewed from a 90-year-old pipe that burst in an industrial area near downtown Los Angeles, leading beaches to close 20 miles downriver in Long Beach, officials said Tuesday.

The top of the 60-inch underground sewer pipe collapsed Monday afternoon, causing a blockage and forcing it to overflow and belch a stinky sludge onto streets and into drains that flow into the concrete-bottomed Los Angeles River.

Workers stopped the spill in a commercial district filled with warehouses around 11 p.m., and cleanup efforts went through the night, said Heather Johnson with LA Sanitation.

Tests of ocean water were conducted at the mouth of the river, about 20 miles south of the spill site, said Nelson Kerr with the Long Beach city health department. Results were not expected until Wednesday.

It was not known how much tainted river water, if any, made it all the way to Long Beach. Kerr said beaches were shut as a precaution and would remain closed until testing shows the water was safe.

The cause of the rupture wasn’t yet known. The pipe dates to the 1920s, Johnson said.

Officials originally estimated that about 100,000 gallons had spilled.

The Los Angeles River begins in the Santa Monica and Santa Susana mountains and winds some 50 miles through Los Angeles County, ending in Long Beach. The river often slows to a trickle as it runs through concrete-bottomed sections near downtown.