The men, Weijing Wang and Piotr Durbajlo, who have both pleaded not guilty, were in court at the start of the trial on Tuesday morning.

Prosecutors requested that the trial be held in secret due to the classified nature of some of the evidence. Though Wang and Durbajlo objected, the court agreed, citing state interests, and journalists were asked to leave.

Wang and Durbajlo were arrested by Polish authorities in January 2019 and accused of spying for China under the cover of seeking business deals for China''s technology giant Huawei.

Wang has been in custody since his arrest.

Durbajlo, a former cybersecurity expert for government agencies including the Internal Security Agency, has been released on bail.

According to the Gazeta Wyborcza daily, the indictment is partly classified, but its public section alleges that Wang is a Chinese intelligence agent and from 2011-2019 sought high-ranking contracts for Huawei that would give the Chinese company insight into, and influence over, Poland''s state and local administration data systems.

He studied in Poland and later served at the Chinese Consulate in Gdansk before moving over to a senior position at Huawei. He is also known by a Polish first name, Stanislaw.

The Pole is suspected of helping him establish contacts and providing him with documents.

If convicted, they face a minimum of three years in prison.

Their trial is expected to take months and there is no date yet for the final verdict.

Their arrests came at a time when the US was exerting pressure on its allies not to use Huawei over data security concerns.

The company has been blocked in the US since 2012 over fears that its equipment is a security risk, and in 2018 Australia, New Zealand and Japan instituted their own bans against using Huawei.