Heightened security at key airports in the aftermath of the Mumbai blasts caused chaos and led to delays of up to four hours in domestic flights on Thursday causing immense hardship to passengers.

Serpentine queues were witnesed at the Delhi airport security check-in with the result that passengers were held up and airline schedules delayed.

At least one Jet Airways [Get Quote] flight to Mumbai was delayed by four hours.

Acknowledging the delays, Civil Aviation Secretary Ajay Prasad said these were caused by the intensified security and was compounded by malfunctioning of some X-Ray machines at Terminal 1-B, catering to private airlines, including Jet Airways, Air Sahara, SpiceJet and Air Deccan.

Prasad is also meeting representatives of the GMR Group and Airports Authority of India officials to review the situation.

Most of the delays occurred at this terminal, where repairs and fresh construction was also being carried out by the newly-appointed GMR-led joint venture company, Delhi International Airport Limited, as part of the first phase of modernisation plan.

This led to cramming of space and caused further delays.

The secondary check being conducted on passengers at the ladder point and the baggage check were leading to flight delays, they said.

Indian Airlines and Kingfisher flights from Terminal 1-A were on an average delayed by 15 minutes to 30 minutes.

Airport officials, however, asked the passengers to understand that "security is not negotiable" and urged them to cooperate.