The greenery-rich design proposals for the main stadium for the 2020 Tokyo Olympics could pose security headaches, an expert said Tuesday.

The Japan Sport Council (JSC) on Monday took the unusual step of disclosing the two proposals now under consideration. It will announce the winner by the end of the year and plans to complete construction by November 2019.

The two designs are described as "technical proposals" and are referred to as Design A and Design B. The JSC did not identify the architects behind them.