A shop manager stood up to three masked raiders who threatened him with a hammer.
Sami Sabet, 48, pressed the alarm as the robbers burst into his shop and sub post office in Beach Gardens, Shoreham.
He locked the door to the post office area as one man grabbed his assistant Laura Battershill.
Two men started kicking and trying to force open the door but Mr Sabet kept forcing it back. They finally broke in and raised a hammer to him, demanding he open the safe.
He refused but they threatened to hit Mrs Battershill, who is in her 20s.
Mr Sabet said: "The alarm was ringing all the time and they ran out of time. They took cash from drawers and left."
Mrs Battershill was hit during the struggle and later taken to hospital and treated for minor injuries.
Mr Sabet said: "I tried very hard to stop them."
The raiders' blue getaway car, MDZ 1488, was followed by police and traced to Lancing Leisure Centre. It is now being checked for evidence.
Detective Inspector Ray Scales, heading the inquiry, said: "We are confident the offenders will be identified and arrested."
Mr Sabet said: "I called Laura and she is fine. She was my main concern when the raiders threatened her."
Mr Sabet said he had been running the shop for the past six months and would not be deterred from carrying on.
Security at the shop would be stepped up.
It is understood the robbers got away with more than £1,000 in the raid, which happened at 4.30pm on Monday.
Witnesses or anyone with information should contact Sussex Police on 0845 6070999.
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