Indian authorities extended a mobile internet blackout across a state of about 30 million people on Monday as police hunted a radical Sikh preacher.

The blackout extension came after supporters of Amritpal Singh were filmed vandalising India's consulate in San Francisco. A similar disturbance also took place in London.

Authorities in the northern state of Punjab launched a major search on Saturday for Singh, who has risen to prominence in recent months demanding the creation of Khalistan, a separate Sikh homeland.

Police said on Monday they had arrested 114 people so far but Singh's whereabouts were unknown.

Protesters hold a photo of Sikh organizer Amritpal Singh as they rally against the Indian government outside the Indian Consulate in San Francisco on March 20. Photo: AFP

The internet outage, originally in place until noon (0630 GMT) on Monday, was extended for another 24 hours.

Videos posted online, and independently verified by AFP, showed men smashing doors and windows at the Indian consulate in San Francisco after they broke down barricades set up outside the building.

The phrase #FreeAmritpal had been sprayed on the property as several dozen protesters gathered outside. Indian media reported that the vandalism had taken place late Sunday.

India registered a "strong protest" with the State Department as well as the US embassy in New Delhi. 

The US government "was reminded of its basic obligation to protect and secure diplomatic representation," the country's foreign ministry said in a statement late Monday. 

Washington "was asked to take appropriate measures to prevent recurrence of such incidents," the ministry added.

The State Department responded by condemning "this weekend's vandalism" and saying it was "committed to the safety and security of these facilities as well as the diplomats who work within them".

New Delhi also summoned the British high commissioner to India, Alex Ellis, on Sunday to voice its displeasure at the vandalism by Singh's supporters outside the Indian high commission in London.

On Monday, flag-waving Sikhs chanting slogans gathered outside the UK embassy in New Delhi.

Punjab -- which is about 58 percent Sikh and 39 percent Hindu -- was rocked by a violent separatist movement for Khalistan in the 1980s and early 1990s in which thousands of people died.

India has often complained to foreign governments about the activities of Sikh hardliners among the Indian diaspora who, it says, are trying to revive the insurgency with a massive financial push.  

Singh and his supporters, armed with swords, knives and guns, raided a police station last month after one of the 30-year-old preacher's aides was arrested for alleged assault and attempted kidnapping.

Indian media quoted security sources as saying Singh was backed by arch-rival Pakistan.

Several police were injured in the brazen daytime raid on the outskirts of Amritsar, home to the holiest Sikh shrine, the Golden Temple, heaping pressure on authorities to act.

Indian authorities frequently shut down mobile internet services, particularly in the restive northern region of Kashmir.