Overnight staff in a western Victoria hospital got a shock when a koala marched into the emergency department.

The koala was caught on security cameras on April 20 and the video was posted on the hospital's website.

The animal was "very casual, very relaxed" according Western District Health's chief executive Rohan Fitzgerald.

"He seemed to know exactly what he was doing," Mr Fitzgerald said.

"After about three minutes, at about 3:30am, he investigated sufficiently and made sure everything was in order and then decided to exit the building."

The animal, nicknamed Blinky Bill, was unable to go into clinical areas which were "secure".

At one point the koala approaches a door, which does not open so he wandered off into another room before trying to get out again.

Hospital staff saw him walking around but just decided to leave him alone.

"Normally we don't have people come into our emergency department that are less than a foot tall," Mr Fitzgerald said.

"He wasn't that obvious to begin with.

"He entered the doors and they've opened automatically for him and that's come into our waiting room."

Mr Fitzgerald said the koala had become a bit of a media sensation and the story had been picked up by several media outlets in the United States.

"We posted it around 14 hours ago, it's had 21,000 views and reached over 57,000 people around the globe.

"I've heard there have been koalas visiting local homes in the area for a number of years now.

"This is the first instance I've seen a koala come into our hospital.

"You never know who you're going to see when you come to Western District Health Service."