Warsaw authorities stepped up security around the city on Thursday ahead of world leaders and officials arriving for Friday and Saturday's NATO summit.
Over 50 delegations from around the world are expected to attend, including U.S. President Barack Obama for what will possibly be his last official European visit.
According to government officials, over 6,000 police, military and security personnel have been tasked with keeping watch over Poland's capital in the coming days.
Poland's parliament tightened anti-terrorism laws in June ahead of the summit and an upcoming visit from Pope Francis, giving security forces the right to more closely monitor the movements of foreign citizens and hold suspects for longer without charges.
The new law gives the state security service the right to conduct surveillance of foreign citizens for up to three months without prior court approval.
Signs were also posted around the city with instructions for citizens on what to do in danger situations. In May, security forces also went through a series of emergency training exercises.
Poland is one of several eastern European states reviewing its anti-terror laws in the wake of recent terrorist attacks, signalling the region's growing concern that it may no longer be immune to the threat.
The country has temporarily reinstated border controls with its European Union neighbours, as well as at ports and airports. Local visa-free border traffic with Russia and Ukraine has also been suspended.