Police shut down a 10-block stretch of Congress Avenue in the heart of downtown early Monday after up to 60 dead birds were found, but a state health official said preliminary air-quality tests showed no dangerous chemicals and that the area should reopen soon.

The carcasses of the grackles, sparrows and pigeons were being tested locally and at the Centers for Disease Control and Prevention in Atlanta, but officials did not believe bird flu was involved or that people are in danger.

"We do not feel there is a threat to the public health," said Adolfo Valadez, the medical director for Austin and Travis County Health and Human Services.

The closure — on the eve of the state's 80th legislative session — came after 40 to 60 carcasses were found overnight along Congress between Sixth and Eighth streets. There were no reports of humans harmed.

Police closed the main north-south route through downtown and all side streets for a block to the east and west while crews tested for environmental contaminants or gas or chlorine leaks, Austin Police spokeswoman Toni Chovanetz said.

The closure extended from 11th Street, which runs in front of the Capitol, 10 blocks south to Cesar Chavez Street at the north end of the Congress Avenue bridge over Town Lake. The Capitol opened on schedule Monday.

A staging area was set up just south of the Capitol, with dozens of fire trucks, police cars and ambulances parked in an area cordoned off by yellow police tape. Some workers donned yellow hazardous-material suits. The staging area is about a block from the governor's mansion, which also remained open.

The entire area was expected to reopen by noon, Valadez said.

He said at least one carcass was being tested locally and others were being shipped to the CDC and Texas A&M University for testing. It could be days or even weeks before the test results come back, Valadez said.

Valadez said the tests will be looking for signs of poisoning or viral infections — though he said officials do not think bird flu is involved.

Federal officials in Washington said they're monitoring the situation.

"There is no credible intelligence to suggest an imminent threat to the homeland or the Austin at this time," said Russ Knocke, spokesman for the Department of Homeland Security.