The UK's major mobile networks have struggled under the strain of those in London rushing to call friends and family as news of a series of explosions spread this morning.
A statement from the UK's largest network operator, Vodafone, said the excessive number of calls had caused outages as the operator set aside capacity for phone calls to the emergency services.
"Following the major incident in London today, Vodafone London switches are at capacity (which is very rare) so we're having to go into 'access overload' procedures, which means freeing up a proportion of capacity across London to ensure the police and emergency services can communicate," the company said.
The operator added the problems should be temporary: "Customers will experience temporary issues making calls but we urge them to keep trying."
The Orange network is also experiencing difficulties, a spokesman for the operator said.
"We can confirm that, due to the number of high calls currently being made on the Orange network, some of its customers in London may experience difficulties making calls on their first attempt and may have to try several times before they get connected," he said.
The problem is affecting the London area most severely, he added, but other areas will experience problems.
An O2 spokesman said the operator is now working to try and overcome the network problems resulting from the morning's explosions.
"The O2 network has not sustained damage due to the explosions in London today. The network is experiencing some congestion in affected areas due to the high volumes of calls. Steps have been taken to increase network capacity," he said.
T-Mobile also reported that its infrastructure is fully functional but that users are set to experience delays to calls.
"There has been no physical damage to our network," a T-Mobile spokeswoman said. "Users can potentially expect congestion and it may take a while to connect." She added that phone calls will also be prioritised.
Rumours that the mobile networks have been shut down to prevent terrorists using mobile phones to detonate bombs appear to have been quashed for the present.
O2's spokesman said: "The government certainly hasn't asked us to put any restrictions on network usage but we will continue to monitor the situation."