Police said pedestrian access to the complex, including public tours, would continue as usual.
Superintendent John Kelly said the changes were a prudent and practical response to US events.
"The situation will continue to be monitored on a daily basis and security measures will be increased or decreased in accordance with worldwide developments," he said.
The decision to beef up security came on the same day as hundreds of people attended a peace rally in Parliament's grounds.
The National Party draped the American flag from its office balcony in Parliament Buildings in defiance of the rally taking place on the forecourt.
But Speaker Jonathan Hunt ordered security guards to take down the flag.
The rally of about 500, including some Government MPs, wanted no retaliation against Afghanistan for last week's attacks in which thousands of people died, saying innocent people would be killed.
"An eye for an eye leaves the whole world blind" and "Afghan blood is the same as USA blood" read two of the placards.
Greens co-leader Jeanette Fitzsimons told the crowd there was no place for revenge or retaliation.
"Killing 5000 unarmed Afghan civilians who have been terrorised by extremists in their own country will not make the score equal."
She was one of four Green MPs at the rally.
Labour and Alliance MPs present included ministers Annette King, Steve Maharey, Matt Robson and Ruth Dyson as well as John Wright, Judy Keall, Steve Chadwick and Phillida Bunkle.
Annette King spoke on behalf of the Government: "We are a country that loves peace. But we are also a country that does not want to see terrorism in the world and I believe we are united in that belief."
Mr Maharey later rejected a suggestion that the strong presence of Government ministers would send a mixed message when he himself had told Parliament that New Zealand might have to go to war to help stamp out global terrorism.
Map: Opposing forces in the war against terror
Pictures: Day 1 | Day 2 | Brooklyn Bridge live webcam
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The fatal flights
Emergency telephone numbers:
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: 0168 1800 932 8555
American Airlines
: 0168 1800 245 0999
NZ Ministry of Foreign Affairs and Trade
: 0800 872 111
US Embassy in Wellington (recorded info): 04 472 2068
Victims and survivors
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