A man with a sledgehammer is thought to have targeted four mosques in Birmingham in a string of attacks.
Reports of a man smashing windows with the tool on Birchfield Road were received at 02:30 GMT, police said.
Officers were then alerted to a similar attack on Slade Road, Erdington, about 45 minutes later.
The damage is being linked to further attacks on mosques in Aston and Perry Barr, West Midlands Police said. The force has yet to establish a motive.
Officers from its Counter Terrorism Unit are investigating.
A spokesperson for Witton Islamic Centre on Witton Road, Aston, said CCTV captures a man smashing windows at about 01:30.
"The whole of the front windows, about six, were smashed," he said.
"Because of the force he used it's gone through the windows and into the mosque itself".
Chief Constable of West Midlands Police Dave Thompson said: "At the moment we don't know the motive for last night's attacks.
"What I can say is that the force and the Counter Terrorism Unit are working side-by-side to find whoever is responsible."
A statement from the Birmingham Council of Mosques said: "We were deeply horrified to hear a number of mosques were vandalised during the early hours of this morning.
"Birmingham's mosques are a place of worship, serenity and a source of peace and tranquillity. We are appalled by such acts of hate/terror."
The council said at least five mosques had been damaged.
Councillor Majid Mahmood tweeted a video of the clean-up taking place at the centre on Witton Road.
Mr Thompson added: "Since the tragic events in Christchurch, New Zealand, officers and staff from West Midlands Police have been working closely with our faith partners across the region to offer reassurance and support at mosques, churches and places of prayer."
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