Holyrood suspends indyref2 debate after Westminster attack
All parliamentary business has now been suspended by the presiding officer Ken Macintosh.
MSPs were debating a motion which would have mandated the First Minister to call a second independence referendum.
Two Police Scotland 4x4 vehicles have now been parked at the entrance of Holyrood Palace, the Queen's official residence in Scotland, across from the Scottish Parliament.
An attacker outside the UK Parliament was shot by police and members of the public have been left injured following a car ramming attack at the nearby Westminster Bridge.
A police officer was stabbed during the incident.
The deputy presiding officer told MSPs: "There are reports of an incident at Westminster.
"Details are still emerging and parliamentary authorities are liaising with Police Scotland and are keeping security under review at Holyrood.
"We will update Members when we have a clearer pictures."
A spokesman for the Scottish Parliament said: "We are aware of a developing situation at Westminster this afternoon and are monitoring matters very closely.
"While there is no intelligence to suggest there is a specific threat to Scotland, Edinburgh or Holyrood we have increased security with immediate effect at the Scottish Parliament as a precaution.
"In the meantime, we would ask all building users to be vigilant whilst going about business and also when leaving or coming to parliament."
Almost all MSPs are in the devolved parliament today and a vote on the First Minister's plans for a fresh independence vote is scheduled for 5.30pm.