Visa appointments were cancelled and members of the public queuing to enter were ordered to leave as the consulate scrambled to react to the incident.
Four police vans and a bomb disposal truck were seen deployed at the sealed-off main entrance, while uniformed police officers were seen donning gas masks outside the building in the busy Central district of the southern Chinese financial hub.
However, the consulate later said the powder was not found to be hazardous.
“We can confirm that an envelope containing white powder was opened inside the Consulate General today,” a spokesperson for the US consulate said.
“The incident has now been resolved. Visa appointments for the rest of the day remain cancelled,” they added.
Police called the incident a “misunderstanding” in a statement Monday.
No dangerous ingredients were found in the powder after an initial investigation and the substance has been collected for further examination, the statement said.
