An "emergency incident" has been reported on the Crimean Bridge, halting traffic on the only link between the annexed peninsula and Russia, a Moscow-backed official said Monday.
Sergey Aksenov, the Russia-appointed head of Crimea, did not specify the nature of the incident.
Last October, a huge blast partially damaged the bridge, causing parts of it to collapse.
"Law enforcement agencies and relevant services are at work. I spoke to the Minister of Transport of the Russian Federation Vitaly Savelyev, and measures are being taken to ameliorate the situation," Aksenov said.
Igor Mikhailichenko, deputy chairman of the Council of Ministers of the Republic of Crimea, has gone to the scene, he added.
Aksenov urged residents and those traveling to and from Crimea to choose an alternative land route.
The nearly 12-mile bridge, also known as the Kerch Bridge, is the longest in Europe and carries both road and rail traffic.
The bridge was severely damaged on October 8 when a fuel tanker exploded and destroyed a large section of the road.
It holds huge strategic and symbolic importance for Russia, which built the 19-kilometer bridge at a cost of around $3.7 billion after Moscow illegally annexed Ukraine's Crimean Peninsula in 2014. It was the physical expression of Russian President Vladimir Putin's objective to take over Ukraine and bind it to Russia forever.
It is a critical artery for supplying Crimea with both its daily needs and supplies for the military, in addition to fuel and goods for civilians.
After the October 8 blast, Russia quickly set about repairs to the span. It was fully reopened to traffic in February.
Earlier this month, Ukraine's Deputy Defense Minister Hanna Maliar made what appeared to be the clearest admission yet that Ukrainian forces were responsible for the October attack.
This is a developing story, more to follow.