The accusations against former electrical engineering students Li Xiaoyu and Dong Jiazhi released on Tuesday include charges of trade secret theft and wire fraud conspiracy.
Prosecutors said the two men spied on a Massachusetts biotech firm in January which was known to be researching possible cures for Covid-19. They also hacked a Maryland company less than a week after it said it was researching Covid-19.
The indictment unsealed in Washington state said the two men - who reside in China - recently "researched vulnerabilities in the networks of biotech and other firms publicly known for work on Covid-19 vaccines, treatments, and testing technology".
The first signs something unusual may be happening at the Houston consulate emerged on Tuesday, when people overlooking the building's courtyard noticed several bins on fire.
Footage shows people throwing what appears to be paper into the bins. It is not known who they were. People were later filmed appearing to pour water on the bins.
Emergency services were called to the building on Tuesday evening. However, the Houston police force said on Twitter officers "were not granted access to enter the building", but did see smoke.