* Evacuation caused by security lapse - police
* Family allowed to proceed despite positive explosives test
* Parts of airport's Terminal 1 evacuated for several hours (Adds number of affected passengers, comments from Lufthansa and Fraport)
FRANKFURT, Aug 7 (Reuters) - Parts of Frankfurt airport were evacuated for several hours on Tuesday following a lapse in security in which a French family of four were allowed to leave the secure zone despite testing positive for explosives, federal police said.
After the alarm had been raised, the family were located in the terminal, re-checked and allowed to continue on their journey after being cleared.
But two gates - A and Z - of the airport's terminal 1 were evacuated and temporarily closed at the airport, a major international hub, disrupting travel during the busy summer holiday season.
"The cause of the evacuation of the terminal was an error by a security officer. Despite a positive test for explosives, a French family of four were allowed to leave the security zone," police said on Twitter.
The police gave no details on what had triggered the original positive explosives test.
At 1230 GMT, police announced that affected parts of the airport, home to airline Lufthansa, had been re-opened, allowing passengers as well as airport and airline employees to return.
Some 1,500 flights had been scheduled for taking off and landing at the airport on Tuesday, according to airport operator Fraport.
Lufthansa said around 7,000 passengers were affected by the disruptions, with a few flights cancelled and some aircraft forced to take off without passengers as a result of the evacuation.
The carrier has booked 2,000 hotel rooms for the night to accommodate affected passengers, it said.
Fraport said operations at Germany's busiest airport had meanwhile restarted, adding that more than 100 staff had helped assist police during the two-hour operation.
The police action came a week and a half after a security scare involving a person who passed through an unmanned checkpoint at Munich airport, Germany's second-biggest after Frankfurt. That triggered an alarm which caused the cancellation of 300 flights and affected more than 30,000 passengers. (Reporting by Till Weber; additional reporting by Nadine Schimroszik, Victoria Bryan and Andreas Cremer; writing by Maria Sheahan and Michelle Martin; editing by Larry King, Richard Balmforth)