The national Democratic Party and a top Democratic super PAC are buying airtime in the Massachusetts Senate special election.

The Democratic Senatorial Campaign Committee and Senate Majority PAC super PAC have each started buying time starting Friday and running through the special election on June 25.

So far, the DSCC's buy appears to be about $750,000, and Senate Majority PAC says its ad buy is at least $500,000. The fact that top Democratic groups are spending money on Rep. Ed Markey's (D) behalf suggests there is at least some concern that the race could be competitive in a deeply blue state.

Most recent polls show Markey leading Republican Gabriel Gomez by single digits. A poll from Democratic-leaning automated pollster Public Policy Polling on Thursday showed Markey ahead 47 percent to 39 percent.

The National Republican Senatorial Committee has not spent money directly on the race, but the state GOP this week helped pay for a second $400,000 ad buy, and national parties sometimes fund ads through state parties. The NRSC has not denied that is the case in Massachusetts.

DSCC spokesman Matt Canter said his party "will take nothing for granted."

"It’s clear that Ed Markey has a strong lead that will grow as voters learn more about Gomez’s support for the national Republican agenda," Canter said.

Senate Majority PAC senior strategist Craig Varoga added: "We will not stand idly by while Mitch McConnell and national Republicans try to use backdoor dollars to buy this race for Gomez.”

Update 9:09 a.m. Friday: The Senate Majority PAC ad is out, and it hits Gomez on his position on reforming Social Security.