Police say a man armed with a knife entered the 24-hour Caltex service station on the Northern Highway at Echuca at 6am.

Police say he walked up to the counter, wielded the knife at the female shop attendant and demanded she hand over money from the till.

Sergeant Kevin Jensen of Echuca police said the woman handed over an amount of cash and the man fled the store.

The incident was captured on CCTV footage and police say they know who the perpetrator is.

Sergeant Jensen said it appeared a 31-year-old man from the Echuca area was responsible.

He said the man had been taken into custody Thursday night for matters of being drunk and disorderly and outstanding warrants.

He was released on bail at 2.30am on Friday. Less than four hours later he entered the Caltex service station and demanded cash.

Echuca police were yesterday looking for the man and said they hoped to make an arrest in the coming days.

At the time of the robbery the service station was quiet and the threat lasted less than a minute. It is not known how much cash was taken.

Anyone with information about the robbery is urged to contact Echuca police on 5482 2255 or Crime Stoppers on 1800 333 000.

Calls can be made anonymously.