DETROIT (Reuters) - Detroit public school children have been forced to switch to bottled water after elevated levels of lead and copper were found at 19 Detroit public schools, or nearly a third of those tested, officials said on Thursday.

The results of water sample tests, released late on Wednesday, raise fears of widespread contamination in the cash-strapped school district, already grappling with severely deteriorated buildings and charges of corruption.

The results also came the same day Michigan lawmakers extended by four months a state of emergency in Flint, about 70 miles northwest of Detroit, to boost aid to authorities managing a crisis over lead contamination in the city's drinking water.

Michelle Zdrodowski, a spokeswoman for Detroit Public Schools, said the district conducted the testing "proactively, because of everything else that was going in the state of Michigan and across the country."

By systematically testing its buildings, at least one of which is more than 100 years old, the district is hoping to avoid the school closures prompted by toxins found in other U.S. cities' school systems.

Last month, water fountains at 30 schools in Newark, New Jersey, were shut off due to elevated levels of lead. In January, the Ohio village of Sebring closed schools for several days due to lead in pipes.

Detroit began collecting water samples at 62 elementary and elementary-middle schools the week of March 28.

Results from the remaining 20 or so buildings, which include middle and high schools, are expected one to two weeks after testing is finished this month, the district said.

The district said the levels of lead and copper found in water samples taken from student drinking fountains and kitchen food-preparation sinks inside 19 schools rose above safety thresholds established by the U.S. Environmental Protection Agency.

The levels varied. At Ludington Magnet Middle School, for example, a sink had lead levels of 67 parts per billion, above the 15 parts per billion threshold set by the EPA.

Each school, however, had elevated lead in one of the three fixtures tested, which Zdrodowski said suggests the toxins not part of a broader problem. Fixes could include replacing fixtures or flushing pipes daily.

The district said it has shut off the drinking fountains in the affected schools and is bringing in more bottled water for students and staff, and posted warnings to avoid drinking the water from bathroom sinks, though students are free to wash to their hands.

(Reporting by Ben Klayman and Eric M. Johnson, editing by G Crosse)