Trespassing

This is a 3 story apartment building.

The tenants have gone away for the weekend and left their door or window open that goes onto the balcony.

It rains and an Owner is concerned about water coming in and the Neighboring Owner wants to put a ladder up and go onto the balcony to close the door or window of the tenant.

Is this permissible or would this be considered trespassing.

There is also a problem that the person attempting to close the door might fall down and be injured or killed when climbing the ladder.

Your advice would be appreciated.!