It was matter of all hands to the pump at the headquarters of a Whanganui security monitoring company immediately after the devastating quake wracked the top of the South Island early on Monday morning.

Wade Coneybeer, general manager of Alarm Watch, said the initial 7.5 quake activated hundreds of alarms across the country, stretching resources at the company's Guyton St headquarters to the maximum.

"From when first big quake struck just after midnight through until 4am our team responded to over 400 high priority alerts when alarms were activated and another 1100 low priority alerts for things like battery failures," Mr Wade said.

"In contrast on the normal Monday morning last week and during the same time period, we responded to 60 high priority alerts and 100 low priority alerts."

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"We monitor thousands of alarms in the country and all of those alarms started activating. The volume of alarms going off was crazy."

Mr Wade was called to go into work to help but he said by the time he got there, more than half a dozen other staff members turned up to help, without being asked.

"These staff members weren't on call, they weren't asked to come in by management. They all just made their way to work because they knew we would be flooded with activity. It's by far the most fulfilling moment I have had at Alarm Watch.

"Those who came in knew their colleagues on shift would be overworked and that our customers would be in need."

He said in the end a total of 10 staff turned up to help.

"One of them had brought her daughter in as she didn't want to leave her at home, so her daughter kept herself busy making hot drinks for the team," he said.