The terminal desk "received a report of an unknown white substance on the floor in the south wing" just after 9 a.m., the authority's Joseph Pentangelo said.
An authority ESU responded, along with hazmat experts who "deemed the substance non-hazardous," he said.
The terminal was completely reopened by 10:10 a.m., Pentangelo said.
The National Guard was activated after the suspicious contents were found in an underground walkway near the terminal entrance at 40th and 8th Avenue, responders said.
Vehicular traffic into and out of the bus terminal was unaffected, although commuters said they were pushed to 9th Avenue.
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