Hollywood hardman Russell tweeted a message sending his love and prayers following the death of two victims and gunman Man Haron Monis in the devastating terror incident at a cafe in Martin Place.
Russell Crowe sent his love and prayers to the victims
He used the hashtag #illridewithyou backing members of the Muslim community, who said they feared reprisals while using public transport.
Russell wrote: "My thoughts go out to the hostages and their families, and to the police and emergency service personnel. #lovesydney #illridewithyou."
Even before police stormed the cafe to free hostages he called on his followers to "stay patient" and await a peaceful resolution.
His friend Hugh tweeted: "The events that have happened in my hometown – Sydney, Australia. Both shocking and tragic. Prayers for all."
New Zealand star Sam Neil added his thoughts, saying: "Sorrow. Calm. Reason. Compassion. Solidarity. Tolerance. Peace. #sydneysiege #illridewithyou".
Australian actress Rebel Wilson told her followers: "Thinking of everyone in Sydney today x"
Sydney is still in shock after the siege
Rebel was at the London premiere of her film Night at the Museum and said that her family had phoned her to say that her two sisters who both work near the scene were safe.
Dexter star Yvonne Strahovski praised her fellow countrymen for their spirit. "United in overcoming intolerance and hate. Absolutely moved by this. #illridewithyou"