The aircraft was flying from Tabuk in Saudi Arabia to Quetta, the capital of Pakistan's Balochistan province.
It was diverted to Karachi after the pilot alerted authorities about the nose wheel problem, Civil Aviation Authority spokesman Pervez George said.
After two attempts, the plane landed at Karachi airport shortly before 10 am local time.
The aircraft's nose wheel failed to deploy and it remained on the airport's main runway hours after the landing.
Footage on television showed the plane standing on the runway.
Officials told the media that the problem had been compounded as the aircraft came down on the main runway, following which the airport was closed to all domestic and international flights.
They did not say how long the airport would remain closed.
Several flights were cancelled and some were diverted to other airports.
Karachi: A Saudi chartered plane with 72 people on board made an emergency landing here on Sunday after developing a nose wheel problem, forcing closure of the city airport for all domestic and international flights.
First Published: Sunday, December 25, 2011, 23:23